The Australian dietary guidelines have been updated for the first time since 2003. Since then there has been a mountain of extra evidence compiled on the risks of eating meat, dairy and eggs. Unfortunately, these guidelines appear to have overlooked many key pieces of evidence that have been published in the scientific literature.
A maximum daily limit of 65 grams of red meat has now been put in place because of the cancer risk associated with it. Also, the recommended maximum protein content in the diet as been reduced from 35 to 25 per cent of total energy. This means that the popular Total Wellbeing Diet no longer conforms to the dietary guidelines. Otherwise, not much has changed with these guidelines - overall, the amount of animal products recommended is about the same.
Did you know that:
- the majority of the world's population is lactose intolerant?
- dairy has been found to raise the risk of prostate cancer?
- iron from meat sources raises the risk of heart disease?
Read our submission to the NHMRC in response to the dietary guidelines below:
Response
to the draft Australian Dietary Guidelines
February 2012
Executive summary
The Australian Dietary Guidelines
play a crucial role in determining the health of the population. They
will influence what is thought to be healthy and culturally
acceptable for decades to come, because they will be taught to
students and medical practitioners, thereby influencing the decisions
and eating habits of the population.
However, in the production of these
draft Guidelines there has been a number of crucial shortcomings in
the Evidence Report and anomalies in the modelling. Additionally,
clarity is needed in the Guide to Healthy Eating. These problems need
to be corrected in order to guide the population’s eating habits to
be more nutrient dense and healthy, and to avoid chronic disease.
I write as someone who has lived
healthily on a wholly plant-based diet for more than ten years. My
comments mostly call into question the amount of animal foods
prescribed for the Australian population, and the methods used to
justify it.
I have classified my findings into
six main topics. These are summarised below.
■ Several of the Foundation
Diets and Total Diets suggested in the Modelling document have
saturated fat content that exceeds the NHMRC’s own recommended
limit of 10 per cent of energy intake.
Also, many of the
prescribed diets that do not exceed 10 per cent saturated fat still
go very close to this level. Even if someone followed the Guidelines
closely, their saturated fat could easily climb above 10 per cent.
This is important because saturated fat is linked to heart disease
risk, and heart disease is the number one cause of death in this
country. An estimated 18 per cent of people are displaying some
symptoms of heart disease risk, and studies show that saturated fat
at 11 per cent of energy may increase the risk of pancreatic cancer.
Therefore, a lower saturated fat limit should be specified, and
adhered to in the modelling.
■ There is a heavy emphasis on
obtaining heme iron (iron from animal flesh), which could increase
risk of heart disease. The Evidence Report did not consider the large
body of evidence on this association. Heme iron is obtained only
from animal products such as red meat, chicken, pork and seafood.
Heme iron has been associated with increase in risk of heart disease
in several large prospective studies. Iron from plant foods
(non-heme iron) is not associated with increased risk of heart
disease. Dietary iron needs can be met sufficiently through plant
foods. Its absorption can be improved with practices such as
consuming adequate vitamin C with each meal.
■ There needs to be definitive
statements about the risks associated with eating red meat. That
red meat increases the risk of colon cancer is no longer seriously
disputed. In addition to the heart disease risk from heme iron
mentioned above, red meat has been associated with the development of
type 2 diabetes in some very large cohort studies. As a minimum step,
the 65 g daily limit on red meat articulated in the Modelling
document should be included in the Guide to Healthy Eating, and the
reasons for it should be highlighted. Given the heme iron association
with heart disease however, this daily limit should be closer to
zero.
■ There is much leeway within
the Guidelines to adopt a high protein diet, which could increase
risk of mortality. In large prospective studies, high protein
diets have been associated with an increase in mortality risk,
independently of saturated fat and other known mortality risks.
■ Dairy should not be
emphasised above its plant-based “alternatives”. This can be
argued on a number of grounds:
a) The majority of the world’s
adults, including Indigenous Australians, are lactose intolerant,
thus an emphasis on dairy is Euro-centric and not representative of
Australia’s cultural diversity.
b) Calcium-fortified dairy
“alternatives” such as soy, rice, almond and oat milk have much
lower saturated fat.
c) Good quality studies have shown
that dairy increases the risk of prostate cancer (the most common
cancer for Australian men) and ovarian cancer.
■ The immense nutritional value
of green and brassica vegetables (and particularly leafy greens)
is not recognised.
a)
In the Guide to Healthy
Eating, green and brassica vegetables appear to be just one option
along with other vegetables. The nutrient dense nature of green
and brassica vegetables means that they really should have their own
food group. They are also strongly protective against cancer.
b) Why is only one serve per day
of green vegetables prescribed in the modelling? It’s curious
enough that green and brassica vegetables were limited to a maximum
of two serves per day in the optimisation because of “cultural
reasons”, but even under this constraint, why was the optimum
number of daily serves of greens one, not two? Including more greens
would be an opportunity to help meet a range of nutritional
requirements such as calcium – but without the saturated fat
associated with other sources of calcium.
c) Within the green and brassica
vegetable grouping, leafy green vegetables have been given
insufficient weighting. Compared with green peas, leafy green
vegetables are much denser in important nutrients such as iron,
calcium and magnesium.
Saturated fat
The NHMRC has set an upper limit
of saturated fat at 10 per cent of energy intake (Nutrient Reference
Values document). This contrasts with the USA’s Food and Nutrition
Board which does not set a tolerable upper limit for saturated fat,
recognising that any incremental increase in saturated fat is known
to raise the risk of coronary heart disease. They recommend that
individuals maintain their saturated fatty acid consumption as low as
possible, while consuming a nutritionally adequate diet (National Academy of Sciences 2006).
Dietary saturated fat has also been linked to increased risk of other
adverse health outcomes such as pancreatic cancer, and it has no
known role in prevention of chronic disease. It is concerning that
several of the sample diets in the draft Dietary Guidelines have
saturated fat content which exceeds the NHMRC’s own limit of 10 per
cent.
Heart disease and saturated fat—still the main
issue
Heart disease is still the number
one cause of death in Australia. In a recent survey, 18 per cent of
Australians reported having symptoms relating to heart disease risk
factors, and this percentage increased with age (Australian Bureau of Statistics 2006).
Mean cholesterol levels as of a few years ago have been estimated to
be 5.1 and 5.2 mmol/L for men and women respectively (Farzadfar et al. 2011).
This is still among the highest in the world – similar to North
America.
A meta-analysis of 61 prospective
studies showed conclusively that total serum cholesterol is related
to heart disease risk (Lewington et al. 2007). Modelling of
experimental data predicts that decreasing saturated fat content by 5
per cent would lower serum cholesterol by about 0.3 mmol/L (Hegsted et al. 1993).
Using the data from these articles, it is clear that a 5 per cent
further reduction in saturated fat content of the diet would achieve
a substantial reduction in heart disease risk among the general
population.
Pancreatic cancer and saturated fat
A large prospective study (Thiébaut et al. 2009)
showed that a group with median intake of 11 per cent saturated fat
had a 21 per cent increase in risk of pancreatic cancer when compared
to lower saturated fat intake, after adjusting for other variables.
The association was strongest for saturated fat of animal origin.
This is one of the best designed studies to date on pancreatic cancer
and fat intake, with 1337 cancer cases and a wide range of observed
fat intakes.
NHMRC’s sample diets exceed
saturated fat limit
Several of the Foundation Diets and
Total Diets have saturated fat content exceeding the NHMRC’s own
recommended limit of 10 per cent of energy intake (see Tables 1 to 3
below). Many of the other prescribed diets that do not exceed 10 per
cent saturated fat still go very close to this level, posing the real
risk of the recommended limit easily being exceeded, even by the most
discerning eater.
Even if the Guidelines were followed
precisely, many people would exceed 10 per cent saturated fat, just
due to natural variation from person to person and the lack of
precise knowledge about fat content in their diets. Very few people
would be able to estimate their saturated fat intake to within one
per cent. Calculations readily show that an extra serve of dairy milk
could raise saturated fat from 10 to 11.5 per cent of energy, and an
extra 40 g serve of cheese could increase it from 10 to 12 per cent.
Clearly, then, it is unwise to prescribe diets with saturated fat
above 9 per cent. A lower target should be aimed for in the diets,
simply to ensure that the majority of people who follow the
Guidelines will actually come under 10 per cent. Reducing the
recommended serves of meat and dairy is an easy way of reducing
saturated fat intake.
Additional calculations
I used the data for energy and
saturated fat in grams from the Tables in Appendix A of the Modelling
document. The percentage energy from saturated fat was calculated
using the accepted figure of 37.6 kJ per gram of fat. When applied to
the Foundation Diets in Tables A11.1 and A11.2, the following results
were obtained, showing levels of saturated fat exceeding or coming
very close to the recommended upper limit.
Saturated fat content of Foundation Diets for women
| Women, from Table A11.1, Foundation Diets |
| Age |
19-30 |
31-50 |
51-70 |
70+ |
| Energy (kJ) |
7383.98 |
7561.16 |
7214.27 |
6586.64 |
| Saturated fat (g) |
17.81 |
17.74 |
19.44 |
19.11 |
| Saturated fat (% energy)* |
9.1 |
8.8 |
10.1 |
10.9 |
*NHMRC’s
recommended upper limit of saturated fat is 10% of energy intake
Saturated fat content of Foundation Diets for men
| Men, from Table A11.2, Foundation Diets |
| Age |
19-30 |
31-50 |
51-70 |
70+ |
| Energy (kJ) |
8943.91 |
8894.29 |
8286.49 |
7304.92 |
| Saturated fat (g) |
22.39 |
22.96 |
21.94 |
19.93 |
| Saturated fat (% energy)* |
9.4 |
9.7 |
10.0 |
10.3 |
*NHMRC’s
recommended upper limit of saturated fat is 10% of energy intake
While these tables represent a low
physical activity level, I found a similar pattern among the 7-day
simulations listed in Appendix 15 of the Modelling document where
higher activity levels are assumed. Using the tables in Appendix 15,
I calculated the mean percentage saturated fat for each grouping of
gender, height/activity level and age. For average height/ light to
moderate activity, the diets in Table were found to exceed 10 per
cent saturated fat on average.
Mean saturated fat content for diet simulations in Appendix 15 of
modelling document – average height, light-moderate physical
activity
Gender/Age
|
Saturated fat (% energy)*
|
Boys 12 to 13
|
10.5
|
Girls 12 to 13
|
10.7
|
Men 70 plus
|
10.2
|
Women 51 to 70
|
10.5
|
Women 70 plus
|
10.6
|
*NHMRC’s
recommended upper limit of saturated fat is 10% of energy intake
Again, while several of the sample
diets do not exceed 10 per cent saturated fat, a number of them lie
in the range between 9 and 10 per cent, which is very close to the
limit.
Summary
The modelling system used to
inform the Guide to Healthy Eating is flawed because the fraction of
energy from saturated fat frequently exceeds 10 per cent, the limit
set by the NHMRC.
Because many of the modelled
diets go close to or exceed 10 per cent of energy from saturated
fat, and there is a strong reliance on animal products, it is to be
expected that many people will go over 10 per cent saturated fat
without being aware of it.
At these levels of saturated
fat it can be expected that there will be additional increases in
the risk of heart disease and pancreatic cancer.
Saturated fat intake can easily
be much lower than 10 per cent of energy while meeting nutrient
requirements. This is achieved through consumption of nutrient-rich
plant foods.
Red meat risks
Unprocessed red meat remains
central to the Australian diet and is still recommended in the new
draft Dietary Guidelines, despite evidence showing serious adverse
health effects. Evidence is accumulating on the potential association
with gastric cancer (González et al. 2006, Cross et al. 2011),
liver disease (Freedman et al. 2010) and renal cancer (Daniel et al. 2012).
The evidence for the link between colorectal cancer and unprocessed
red meat is convincing and uncontroversial. There also exists a large
amount of data on the positive association between unprocessed red
meat and type 2 diabetes. Further discussion on the latter two
diseases follows below.
Colorectal cancer
Every meta-analysis of prospective
studies published in the international peer-reviewed literature in
the last ten years has found a statistically significant positive
association between red meat and colorectal cancer (Sandhu et al.
2001, Norat et al. 2002, Larsson & Wolk 2006, Chan et al.
2011, Alexander et al. 2011 and World Cancer Research Fund /
American Institute for Cancer Research 2007). Only Alexander et al.
(2011) downplayed their result due to heterogeneity of studies;
however, heterogeneity generally makes it harder to detect an
underlying association. This only confirms the robustness of the
finding.
Two of these studies existed prior
to the release of the previous edition of the Dietary Guidelines,
however they appear to have escaped the notice of the authors at the
time. The previous version of the Guide to Healthy Eating (1998),
which is still current, suggests that up to 200 g daily serves of red
meat is healthy. As a result, many people erroneously believe this to
be the case – with potentially tragic health outcomes.
The document “A review of the
evidence to address targeted questions to inform the revision of the
Australian Dietary Guidelines” (the Evidence Report) states
that the evidence linking red meat to colorectal cancer is in Grade B
(probable). Given the history of investigation stated above, it is
not clear why the evidence is not Grade A (convincing
association). The disease burden associated with colorectal cancer is
significant and every effort is needed to reduce it.
Type 2 diabetes
In recent years there have been a
number of large prospective studies on the link between red meat and
diabetes. Of three recent meta-analyses conducted, two returned a
statistically significant link between red meat and type 2 diabetes
(Aune et al. 2009, Pan et al. 2011). The latter of these
(and the most up-to-date) included 28,228 cases of type 2 diabetes.
Their estimate of the effect is a 19 per cent increase in risk of
type 2 diabetes per 100 g of unprocessed red meat.
The meta-analysis by Micha et al.
(2010) did not return a statistically significant result; however, a
number of large cohort studies appeared just after that paper was
written, such as Steinbrecher et al. (2011) which included 8587
incident cases of type 2 diabetes. This alone would increase the
number of cases in that meta-analysis by 80 per cent.
In Australia, around 1.7 million
people have type 2 diabetes and a further 2 million people have a
pre-diabetes condition (source:
http://www.diabetesvic.org.au).
This is about one person in six. Therefore, including red meat in the
Dietary Guidelines is particularly inappropriate for at least one in
six people in Australia on account of diabetes risk.
Getting
iron and zinc
It is often
suggested that iron from animal flesh is the most reliable way to
avoid iron deficiency anemia. Yet, the majority of the population’s
iron intake comes from plants (Australian Bureau of Statistics 1998).
The bioavailability of non-heme iron (mostly from plants) can be
improved markedly by simple practices such as consuming vitamin
C-rich food with a meal and avoiding tea with a meal (Thankachan et al. 2008).
Some studies of young women among well-nourished populations have
shown little relationship between iron intake and the incidence of
anemia (Pynaert et al. 2007, Asakura et al. 2009). Also, it
has been found that the rate of iron deficiency anemia is not
markedly different between vegetarians and non-vegetarians (Ball & Bartlett 1999).
Good sources of iron from plant sources include legumes, whole
grains, dried fruits, leafy green vegetables, nuts and seeds.
The recommended daily intake of zinc
for Australian men is set at 14 mg per day, with up to 50 per cent
extra said to be required in the case of plant-based diets (Nutrient
Reference Values document). This recommended daily intake for zinc is
one of the highest in the world, despite there being little evidence
of zinc deficiency in Australia. In Canada and the USA the
recommended daily intake is 11 mg per day. The World Health
Organization set a recommended nutrient intake of 14 mg per day only
for the extreme case of high phytate diets with very low
bioavailability.
Zinc is readily available from foods
across the plant kingdom, including grains, legumes, seeds, nuts and
vegetables. Examples include peanut butter, green beans, zucchini,
chick peas, pumpkin seeds, whole wheat, rice and oats.
Bioavailability is improved substantially by practices that are
already common in food preparation which reduce the phytate content.
This includes using yeast in bread making, soaking or sprouting (in
the case of legumes), and roasting (of nuts and seeds). It is not
hard to obtain iron and zinc from a plant-based diet.
Summary
The Modelling document placed
serve limits on red meat at 65 g per day. The previous version of
the Guide to Healthy Eating suggested that 200 g per day was
acceptable, so this is a major change. This change, and the reasons
for it, has not been communicated clearly enough in the new Guide to
Healthy Eating. There is nothing in the Guide to Healthy Eating to
indicate that when people eat red meat they are taking on additional
risk for chronic disease depending on their level of intake.
It is a concern that the
Guidelines recommend eating red meat at all given that it has been
convincingly associated with cancer and other chronic disease.
Red meat is particularly
inappropriate for at least one in six people in Australia on account
of diabetes risk.
Iron and zinc can be obtained
from plant foods by following some simple guidelines.
Coronary heart
disease and cardiovascular disease: the link with heme iron from meat
Dietary iron comes in two forms:
heme and non-heme. Plants contain only non-heme iron. Heme iron is
only obtained from animal products, the main ones being red meat,
chicken, turkey and seafood.
Dietary heme iron has been shown to
be associated with coronary heart disease or cardiovascular disease
in several large prospective studies (Ascherio et al. 1994, Klipstein-Grobusch et al. 1999,
Lee et al. 2005, van der A et al. 2005 and Qi et al. 2007).
These studies included several tens of thousands of people. The
latter study found that a high dietary heme intake was associated
with a 50 per cent increase in risk of heart disease.
Recently, a large cohort study with
over 21,000 participants found an association between red meat
consumption and coronary heart disease (Ashaye et al. 2011).
This may also be due to the heme iron mechanism. A similar finding
was documented in Kelemen et al. (2005), where a study of 29,017
women showed a 44 per cent increase in coronary heart disease risk
for the highest versus lowest red meat intake.
It is surprising that the Evidence
Report did not examine the evidence linking heme iron and heart
disease. Heart disease is still the number one cause of death in
this country. The evidence on heme iron and heart disease risk
should be comprehensively examined and dietary advice should be
modified accordingly. Plant foods can meet dietary iron needs
adequately. Therefore, heme iron from animal flesh should be avoided,
resulting in lower heart disease risk.
Summary
Heme iron, obtained from animal
flesh, has been associated with an increased risk of heart disease
in a number of large cohort studies.
This increase in risk is
especially important since heart disease remains the number one
cause of death in Australia. The evidence suggests that wherever
possible, heme iron (derived from meat products) should be avoided.
Non-heme iron from plants can
meet iron needs adequately.
High protein
diets
Since the release of the
previous Dietary Guidelines there has been an increase in the number
of books and programs advocating a high protein diet. Data is
beginning to emerge on the long-term adverse consequences of these
diets.
In a large prospective study of more
than 40,000 women over a 12-year period, protein intake was
associated with cardiovascular mortality. Among women aged 40—49 at
enrolment, the increase in cardiovascular mortality risk was 16 per
cent per decile of protein intake (Lagiou et al. 2007). The
study corrected for saturated fat intake and other factors. This
increase in mortality risk could be due partially to heme iron
(derived from animal flesh), as already mentioned.
Another study of 43,960 men found
that among healthy men, there was a 21 per cent increase in risk in
ischemic heart disease for the highest versus lowest quintiles of
total protein intake (Preis et al. 2010). This result was due
almost entirely to animal protein; no association was found for
vegetable protein.
The Nutrient Reference Values
document sets an upper limit for protein at 25 per cent of total
energy. This upper limit of protein has been reduced from 35 per cent
in the previous Dietary Guidelines. High protein diets, such as the
one in Noakes et al. (2005) that led to the Total Wellbeing diet book,
are no longer valid within the Dietary Guidelines – not only
because of the extreme protein level, but also because of the large
daily serves of red meat which are known to raise colorectal cancer
risk.
However, a diet with 25 per cent
protein is still well within the high range of those long-term cohort
studies mentioned above. These protein amounts are excessive: the
population mean is around 16—17 per cent. The available data
indicates an increase in mortality risk at protein levels of 25 per
cent of total energy.
Summary
The draft Dietary Guidelines and
Guide to Healthy Eating do not rule out the possibility of high
protein diets which have been shown to be associated with chronic
disease and mortality risk in the long term.
Dairy
The Guide to Healthy Eating
emphasises dairy intake and effectively gives dairy a food group of
its own, albeit with “alternatives” that are not clearly defined.
However, in addition to its saturated fat content, the intake of
dairy has been shown to be associated with chronic diseases and other
adverse conditions.
Lactose intolerance
The ability of humans to digest
dairy milk is a relatively recent genetic adaptation. The condition
known as lactase persistence is the ability to digest lactose
from milk as an adult. Worldwide, the majority of the population
(approximately 65 per cent) does not have this ability, and is
lactose intolerant. Within certain ethnic groups the prevalence of
lactose intolerance is very much higher. This includes Aboriginal
Australia, southern Africa, China, Japan, south-east Asia, Indonesia
and Papua New Guinea (Itan et al. 2010).
Clearly, an emphasis on dairy milk
to obtain calcium represents a limited Euro-centric viewpoint. While
the Guidelines make some suggestions for people who are lactose
intolerant, these are not backed up by model results. None of the
diets in the Modelling document reflect a lactose intolerant diet;
hence, the draft Dietary Guidelines do not meaningfully consider
large sections of the diverse Australian population.
Prostate cancer and dairy
Studies show an increased risk of
prostate cancer with dairy consumption. The Evidence Report cites
only the “poor quality” literature review by Alvarez-León et al.
(2006). This review doesn’t consider the findings in the
meta-analysis by Gao et al. (2005) which was conducted on
prospective studies and found that high intake of both dairy and
calcium was related to increased risk of prostate cancer. They found
a 33 per cent increase in risk of prostate cancer for the highest
versus the lowest categories of dairy intake. A similar association
was observed in a subsequent prospective study of 43,435 men over 7.5
years (Kurahashi et al. 2008). On what basis were these two
publications excluded from the NHMRC’s Evidence Report?
The link between dairy and prostate
cancer is also seen in case-control studies (Qin et al. 2004)
and ecological studies across many countries (Ganmaa et al. 2002).
More recently, a large prospective
study of 27,111 participants found that intake of phytanic acid
(found in dairy products and meat) was related to an increased risk
of prostate cancer (Wright et al. 2011).
Laboratory tests have shown that
dairy milk stimulated the growth of prostate cancer cells in culture,
increasing the growth rate by over 30 per cent, while almond milk
decreased the growth rate by 30 per cent (Tate et al. 2011).
Within the 7-day sample diets that
form the basis of the Dietary Guidelines, adult men have average
calcium values ranging from about 1340 to 1780 mg per day, depending
on age group and activity level. Sample diets for boys aged 14–18
with high activity level have average calcium nearly 1900 mg per day.
The recommended daily intake already has a considerable safety
margin, and exceeding the recommended daily intake to this extent (by
40 to 60 per cent) is unnecessary. The large amounts of dairy used to
deliver these quantities of calcium are likely to be enhancing
lifetime prostate cancer risk.
Prostate cancer is the most common
cancer for men in Australia. One in nine men will develop the disease
in their lifetime (source:
http://www.prostate.org.au).
Given this disease burden, the advice on dairy intake should be
reconsidered urgently.
Ovarian cancer and dairy
Over time, a number of studies have
reported a suggestive association of ovarian cancer risk with the
intake of lactose. Two meta-analyses published in 2006 independently
reported a statistically significant increase in cancer risk for
higher lactose intake (Larsson et al. 2006, Genkinger et al. 2006).
The former of these studies reported a 13 per cent increase in risk
of ovarian cancer for each 10 g increase in lactose.
In addition, suggestive associations
have been found between the risk of ovarian cancer and the intake of
fat from animal sources. Recently, in a very large study of 151,552
women over a period of 9 years, 695 cases of ovarian cancer were
observed, and the risk of ovarian cancer was found to be related to
the intake of animal fat (Blank et al. 2012).
Dairy and severe acne
Acne is not considered to be a
chronic disease, however it is a major concern for many young people
and can leave lifelong scars. Large prospective studies have shown
that dairy intake increases the risk of severe acne in a
dose-dependent manner (Adebamowo et al. 2005, Adebamowo et al. 2006).
The risk was found to be higher for low fat milk. This is a
particular concern because the Guide to Healthy Eating places an
emphasis on low fat dairy products.
Alternative sources of calcium
The draft Dietary Guidelines and
Guide to Healthy Eating do not devote much space to discussing the
“alternatives” within the dairy grouping. Due to the high
saturated fat content and the diseases associated with dairy (i.e.
milk, yoghurt and cheese), the calcium-fortified “alternatives”
are almost invariably a better choice. A serving of calcium-fortified
soy milk typically has less than one quarter of the amount of
saturated fat as dairy milk. There are other choices available, such
as oat, rice and almond milk.
There are many other foods that can
contribute to daily calcium requirements. From the nuts and seeds
group, tahini (sesame seed paste) and ground flax seed have about the
same calcium content per gram of saturated fat as whole milk. Also,
compared with whole milk, chia seeds contain about 3 times the amount
of calcium per gram of saturated fat. Chia seeds are grown in
Australia and are readily available in supermarkets nowadays.
Within the legumes group, certain
kinds of beans have more bioavailable calcium and can contribute a
substantial fraction of daily needs. These include white beans and
chick peas (Sahuquillo et al. 2003). These legumes can also
contribute useful amounts of iron and zinc.
The nutrient density of leafy green
vegetables places them in a category of their own. They differ
markedly from other vegetables, even green peas. This is shown in Figure ,
where it can be seen that leafy greens have much higher calcium for
the energy content. They are also more calcium-dense than dairy milk.
They can be a significant source of calcium without the saturated
fat. My own experiments with linear programming and the AUSNUT07
database indicate that calcium requirements can be met by generous
consumption of leafy greens along with other plant foods.
While calcium bioavailability does
vary between foods, it can be seen that a wide variety of foods can
be used to meet daily calcium needs.
Calcium content per unit energy (mg/kcal) of selected foods, USDA
Nutrient Database
Summary
The draft Dietary Guidelines’
emphasis on dairy neglects the prevalence of lactose intolerance in
the Australian community.
There are chronic disease
associations with dairy intake (prostate cancer, ovarian cancer).
The sample diets that form the basis of the Guidelines exceed the
recommended daily intake of calcium by up to 60 per cent. The amount
of recommended dairy is excessive and is likely to be enhancing
cancer risk.
Studies show that dairy intake
may increase the risk of severe acne.
Calcium can be obtained from a
wide variety of plant sources with less saturated fat than dairy.
Due to the chronic disease risk
associated with dairy consumption, and to reduce the saturated fat
content of the diet, it would be prudent to promote calcium-rich
plant foods and calcium-fortified alternatives to dairy.
Green
vegetables
The Foundation Diets and many of
the sample Total Diets include only one serve of green and brassica
vegetables per day. Also, the modelled composite serve of greens has
a large proportion of green peas and beans, which are less dense in
calcium and magnesium than leafy greens (although they are extremely
good sources of zinc). A further complication is that the Guide to
Healthy Eating effectively groups green and brassica vegetables with
all other vegetables, which could be taken to mean that they are in
some way equivalent. This may stem from some of the modelling work,
where a severe limit was placed on the green vegetable grouping.
Modelling questions
The Modelling document states that
the number of daily serves of green and brassica vegetables was
limited to two in the optimisation (Table 4). The stated reason for
this was that the nutrient-dense nature of green vegetables caused
them to become too dominant, and that any more serves would not be
culturally acceptable.
It is disappointing that this
arbitrary suboptimal constraint was imposed. At least three serves
are achievable by anyone, and some people may choose to eat more if
they knew about the benefits. Culturally, we are not homogenous –
for example, people of Asian background tend to eat more leafy green
vegetables (Butler et al. 2010). Eating more green vegetables
(and especially leafy greens) should be encouraged, not stifled.
Limiting green vegetables in this way not only denies the opportunity
for healthier diets but also ignores Australia’s diverse cultural
makeup.
Nevertheless, given the upper
constraint of two serves per day, it is unclear why the Foundation
Diets and many of the sample Total Diets only prescribe one serve
per day (as shown in Tables 11 and 12 of the Modelling document).
Why wasn’t the optimal number of green vegetables two serves per
day?
Green and brassica vegetables have
potent anti-carcinogenic properties (Boivin et al. 2009). There
is an opportunity here to improve health outcomes, simply by allowing
these nutrient-dense foods to take their proper place in the diet.
Summary
Leafy green vegetables are more
nutrient dense in calcium, magnesium and iron than full-fat and
low-fat dairy.
The decision by the modellers
to severely restrict the amount of green and brassica vegetables in
their model means that their nutrient density (particularly calcium
density) will not be seen for what it is.
In the Guide to Healthy Eating,
green and brassica vegetables appear to be just one option amongst
all other vegetables. A reader could take this to mean that all
vegetables are essentially equivalent—they are not.
In terms of public education,
the best way to communicate the benefits of green and brassica
vegetables is to give them a food group of their own, with a strong
emphasis on leafy greens.
Concluding remarks
Many
statements in the Modelling document stress “cultural
acceptability”. These Guidelines will be influencing what is
culturally acceptable for decades to come, because they will be
taught to students and medical practitioners, thereby influencing the
eating habits of the population.
Some questionable modelling
decisions were taken that essentially reinforce the status quo of
high saturated fat intake. The continued reliance on animal products,
and the trivial amounts of green and brassica vegetables in these
diets, means that high saturated fat will remain firmly entrenched.
It appears that these modelling decisions were made so as not to
overly challenge the average person as measured by a survey of eating
habits in 1995.
Saturated fat, and its association
with heart disease, is still the main issue in the Australian diet.
Nevertheless, it appears that the modelling did not explicitly
attempt to cap the saturated fat content. This means that in
practice, many people with good dietary intentions will have
saturated fat intake well above 10 per cent of energy. Few people can
accurately estimate the saturated fat content of their own diet. The
exhortations to choose low-fat dairy are ineffective because the
marketing of low fat and fat reduced products bears little
relationship to the actual fat content. Also, low fat products often
have added sugar to entice the consumer. This, along with
“discretionary” serves of sausages, bacon, eggs, cream and so on,
is likely to lead to a poor result.
The Evidence Report failed to
examine some chronic disease links for which there is a large amount
of evidence. Heme iron from animal flesh contributes to heart disease
independently of the saturated fat link. In addition, continued
reliance on animal products for many people is likely to lead to
chronic disease such as cancer (pancreatic, colon, prostate, ovarian)
and type 2 diabetes.
Final remark: getting vitamin B12
Vitamin B12 is made from bacteria
and is not reliably available from plants. This is often cited as a
reason not to abandon eating meat, dairy and eggs. However, the
prevalence of B12 deficiency is very high in older Australians: 23
per cent of people aged 50 or over (Flood et al. 2006). Clearly,
it is not the lack of animal products in the diet that has caused
this high rate of deficiency. Supplementation is a very good idea for
omnivores, vegetarians and vegans.
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