Sunday, February 5, 2012

DGA 2011 - Dairy and Alternatives

2.5 Milk, yoghurt, cheese and/or alternatives (mostly reduced fat)

Vitamin D - 1 µg = 40 IU
25-Hydroxyvitamin D - 2.5 nmol/l = 1 ng/ml

Full Fat or Low Fat?

“It is probable that the consumption of at least two servings per day of dairy foods (milk, cheese and yoghurt) is associated with reduced risk of ischemic heart disease and myocardial infarction (Grade B, Section 5.3 in Evidence Report [14]) [376].”

“It is probable that the consumption of two or more servings of dairy foods per day (milk, cheese and yoghurt) is associated with reduced risk of stroke (Grade B, Section 5.4 in Evidence Report [14]) [376, 377] particularly reduced fat varieties.”



The ‘particularly reduced fat varieties’ was not the conclusion of either paper.  The 376 paper did not want to make conclusive recommendations on the differences in health between whole milk and reduced fat milk for the following reason:

“Nevertheless, persons who choose to drink fat-reduced milks will almost certainly have adopted other “healthy’ behaviours, and these will undoubtedly be responsible for further confounding. These other factors cannot all be known, but they will be responsible for biases, which cannot possibly be estimated or allowed for. No reasonable conclusions can therefore be based on these data and we refrain from conducting any kind of meta-analysis or summary statistics.”

Generally observational studies find people who drink reduced fat milk have lower odds ratios potentially confounded by other healthy behaviours.  They did mention one study that found:

“In another case-control study the odds ratio for MI were significantly reduced (0.36; 0.13, 0.99) in subjects within the top quartile of adipose tissue C15.0 levels.”

The 15:0 fatty acid is found in ruminants and so can be used as a marker of dairy fat (and ruminant fat) consumption.  The more dairy fat consumed the more 15:0 will likely end up in adipose tissue.  Those in the top quartile would have likely consumed more full fat dairy and whole milk.  This study at least suggests that dairy fat is inversely associated with myocardial infarctions.  The authors conclude with:

“In the absence of evidence from large randomised trials the statement of German and Dillard is therefore most apposite: “Such hypotheses (about fat-reduced milks) are the basis of sound scientific debate; however they are not the basis of sound public health policy’.”

The authors of the 377 paper conclude by saying:

“We observed no statistically significant associations in this large cohort between intake of total fat, specific types of fat, or cholesterol and risk of ischaemic, haemorrhagic, or total stroke. In addition, consumption of red meats, high fat dairy products, nuts, or eggs did not seem to be related to risk of stroke.”

It appears the dietary guidelines have misrepresented the studies they cite.  One study concluded by saying that without RCTs, recommending reduced fat milk is not the basis of sound public health policy, the other found total fat, types of fat and high fat dairy to not be related to the risk of stroke.

“The proportion of total fat and saturated fat content in some milk, cheese and yoghurts has led to the recommendation that reduced fat varieties should be chosen on most occasions.”

The guidelines in section 3.1 to recommend reducing saturated and total fat consumption, but the cited studies don’t support either recommendation.  Instead they find low carbohydrate, high fat diets are equal to or better than low fat, high carbohydrate diets for weight loss [1] and that dietary fat improves blood lipids relative to carbohydrate [2].  Saturated fatty acids are also not associated with cardiovascular disease [3] and are inversely associated with atherosclerosis [4].

“Two proposed mechanisms link the consumption of milk, yoghurt and cheese products with a reduction in cardiovascular risk. Firstly, the consumption of milk, yoghurt and cheese products has been linked to an increase in the levels of high density lipoprotein (HDL) cholesterol.”

This proposed mechanism is out of touch with the recommendations.  HDL-C is increased by dietary fat, especially saturated fat, relative to carbohydrate [2].  Therefore the increase in HDL-C, the proposed mechanism by which dairy reduces the risk of cardiovascular disease, is proportional to the total dairy fat consumed.

Full fat dairy may be preferable to reduced fat dairy as dairy fat is rich in fat soluble vitamins such as A, D and K2, and also contains health promoting fats such as butyric acid (4:0) and other short to medium chain fats, long chain omega 3 PUFA and healthy trans-fats such as vaccenic acid and conjugated linoleic acids.

Butyric acid comprises 3-4% of dairy fat and short and medium chain fats comprise roughly 11-12% of dairy fat [5].  Butyric acid is likely to be the main reason why soluble fibre is healthy.  (Those values may be roughly 50% higher if grass-fed, which is based on assumptions that dairy in the USDA database are from grain-fed cows, the milk from the sheep and goats are grass-fed and the physiology between the species is not significantly different).  Soluble fibre is fermented by bacteria in the colon and butyric acid is a by-product, the butyric acid then nourishes the colon as its primary fuel source.  Butyric acid decreases inflammation [6] intestinal permeability [7] and is preventative against weight gain and insulin resistance [8].  Short and medium chain fats (4-12 carbon length) are more likely to be converted into ketones.  Ketogenic diets increase mitochondrial biogenesis [9], which may be therapeutic for a number of metabolic, age-related, neurodegenerative and psychiatric diseases [10].  Medium chain fats may also aid in weight loss by increasing fat metabolism and thermogenesis [11].  (This evidence also supports the consumption of coconut-based foods, which is the richest source of medium chain triglycerides).  Long chain omega 3 PUFA don’t need a mention and I’ve discussed the healthy trans-fats previous.

Vitamin K2 is an underappreciated and relatively unheard of essential fat-soluble vitamin.  Fatty meats, organ meats, eggs and cheese are the best sources and are in the form of menaquinone-4, vitamin K2 can also be found in some fermented foods as menaquinone-7 [12].  Vitamin K2 is responsible for activating vitamin A and vitamin D dependent proteins [13], moving calcium from soft tissue such as artery walls to use it in mineralising bones [14], which makes it effective at preventing both cardiovascular disease [15] and osteoporosis [16], as well as other functions in several organs such as the brain, pancreas and salivary glands [17].  The health benefits from vitamin K2 are not seen with vitamin K1 (phylloquinone) consumption [15].  Humans do not convert vitamin K1 into K2 and the K2 from intestinal bacteria is barely absorbed.

As a fat-soluble vitamin its intake depends on the quantity of fat consumed.  Americans, like Australians, have been told to reduce animal fat and cholesterol for decades.  With the saturated fat/cholesterol phobia we have cut the fat off our meat, stopped eating organ meats, choose reduced fat dairy and throw out the yolks, which leaves cheese.  Cheese is negatively associated with CHD and is a major source of K2 our diet [15].  This is probably because it’s now our major source of animal fat.  Even reduced fat cheddar cheese would have a fair amount of K2 are it is roughly 16-24% fat by weight.  Vitamin K2 is one factor that can explain why dairy is inversely associated with cardiovascular disease.  What’s also interesting is that vitamin K2 must have a very beneficial effect on health to overcome confounding variables related to its consumption and unhealthy lifestyles.

“In contrast to phylloquinone, intake of menaquinone (mainly MK-4 from eggs and meat, and MK-8 and MK-9 from cheese) is not related to a healthy lifestyle or diet, which makes it unlikely that the observed reduction in coronary risk is due to confounding.” [15]

The Value of Dairy, Calcium and Vitamin D

Despite being concerned with whole food rather than nutrients, the guidelines focus almost exclusively on calcium in regards to dairy consumption.  This is demonstrated by:

“The traditional nutritional rationale for the inclusion of dairy foods such as milk, cheese and yoghurt is their high calcium content and the positive relationship between calcium and bone mass.”

“Alternatives to milk, cheese and yoghurt include calcium-enriched legume/bean milk products such as calcium enriched soy drinks.”

However, these alternatives to dairy foods are very different nutritionally.  Calcium enriched legume milk products may compare well on calcium, but they likely do not contain vitamins A, B12, D and K2, long chain omega 3’s and conjugated linoleic acids [5].  As discussed above vitamin K2 is an essential nutrient and very useful in preventing arterial calcification and osteoporosis.  Without vitamin K2, calcium enriched foods may similarly increase the risk of myocardial infarction as calcium supplements do.

If calcium enriched foods aren’t an alternative to dairy, then what is?  There are people who have lactose intolerance or allergic reactions to dairy proteins.  Dairy is included in the diet mostly for calcium, but there are more factors involved in calcium balance and bone mineral density than just dietary calcium.

Vitamin D greatly increases calcium absorption.  Calcium absorption is 65% higher when vitamin D blood levels are at 86.5 nmol/l, relative to 50 nmol/l.  Both vitamin D blood levels are in the reference range, but the authors consider this to be a sub-optimal range for calcium absorption, instead they suggest the reference range for 25-hydroxyvitamin D should be 80-90 nmol/l [18].  If a young or middle aged adult increased their calcium absorption by 65% the RDI could effectively by lowered from 1,000 mg to 606 mg for them.  Even without an emphasis on vitamin D our calcium requirement for men and women may be 741 mg [19].  This now means increasing vitamin D could reduce the requirement down to 449 mg (~450 mg).  Now consider that 2.8% of New Zealanders aged 15 and over have a vitamin D deficiency (17.5 nmol/l) and 27.6% had a vitamin D insufficiency (37.5 nmol/l), or that the Geelong Osteoporosis study found the average vitamin D levels in summer were 70 nmol/l and in winter were 56 nmol/l [20].  Even 70 is below the current 75 nmol/l cut-off for vitamin D sufficiency.  Not many Australians have ideal vitamin D blood levels if ideal is 80-90 nmol/l (perhaps 80 in winter and 90 nmol/l in summer).  What is evident is that Australians and New Zealanders have a large room for improvement in increasing calcium absorption.

We may have low vitamin D blood levels because the adequate intake (AI) is too low.  The AI is 5 µg for people 50 years and younger, 10 µg for people aged 51-70 and 15 µg for people aged 70+.  The upper level is 25 µg for infants and 80 µg for everyone else [20].  The AI may be good enough to prevent rickets but isn’t high enough to achieve optimal calcium absorption.  One study found most people were able to reach 100 nmol/l with about 100 µg of vitamin D and 240 µg was needed for 97.5% of the population to have a vitamin D blood level of 100 nmol/l, while not toxicity occurred from vitamin D intakes of 250 µg [21].  The intake of vitamin D needed for 100 nmol/l of 25-hydroxyvitamin D varies greatly between individuals and depends on factors such as body weight [22].  Vitamin D toxicity occurs when 25-hydroxyvitamin is over 200 nmol/l, which requires an intake of 1,000 µg per day [23].  Maximum vitamin D intake from sunlight is only 500 µg per day [23], therefore it’s unlikely that vitamin D toxicity could occur naturally, unless one is either vitamin A or K2 deficient [24].

Current sun exposure guidelines may be too conservative and largely contribute to the widespread low levels of 25-hydroxyvitamin D in Australians.  Vitamin D has potent anti-cancer effects.  UVA is responsible for skin cancers and depletes vitamin D, while UVB is used to synthesise vitamin D.  UVA is around all day and can penetrate glass, clothing and sunscreen; UVB is only around while the UV index is greater than 3 and does not have the same penetrance [25].  Taking all of this into account it seems that the UVA:UVB ratio is predictive of skin cancer and is best kept low.  Sufficient midday sun exposure to as much of the body as possible to meet the vitamin D targets outlined above, while minimising sunscreen, and sunlight exposure through windows and clothing will keep the UVA:UVB ratio low, ensure good vitamin D levels and reduce the risk of osteoporosis and skin cancer and other forms of cancer.

The authors of the 376 study dismiss the idea that because our hunter-gatherer ancestors had strong bones without consuming dairy, therefore we don’t need to consume dairy either.  They dismiss it on the basis that our diet has changed.  Indeed it has changed.  Most Australians consume a highly refined diet largely devoid of key nutrients for bone health (such as vitamin K2), have poor vitamin D levels from limited sun exposure and we now also consume a grain-based diet, which reduces calcium absorption from phytic acid and compromises vitamin D metabolism [26].  A return to a diet and sun exposure based on our hunter-gatherer ancestors could produce strong bones without needing dairy.

An alternative to dairy would therefore include optimal vitamin D from mostly sunlight (to enhance calcium absorption) and other foods that have similar nutrients as dairy foods do, while assuming one consumes the recommended amount of fruit and vegetables.

“Milk, cheese and yoghurt are a good source of many nutrients, including calcium, protein, iodine, vitamin A, vitamin D, riboflavin, vitamin B12 and zinc.”

Foods that are food sources in these nutrients (except calcium) are other animal-based foods, such as meat, fish (including shellfish), eggs and organs.  All have highly bioavailable protein, with a complete amino acid profile and include nutrients derived from amino acids such as carnitine, carnosine, creatine, glutathione and taurine.  Fish, eggs and organs are good sources of iodine, eggs and liver are good sources of vitamin A.  All are good sources of riboflavin, vitamin B12 and zinc as well as vitamin B5, K2, selenium and long chain omega 3’s (which dairy is also a good source of).  Meat from ruminant animals is also a good source of the healthy trans-fats, vaccenic acid and conjugated linoleic acids.  Many of the nutrients listed above are found abundantly in other animal foods and animal foods are often the only good or unique source of them [5].

This suggests that an alternative to dairy is not calcium-enriched legume milks, but rather animal foods and ideal levels of vitamin D.  Although if dairy is replaced with animal foods and vitamin D in the context of a highly refined diet low calcium could become a problem, but in a highly refined diet health problems are ubiquitous anyway.

Conclusion

Raising HDL-C and vitamin K2 are some mechanisms that may explain how dairy foods decrease the risk of cardiovascular disease.  These mechanisms are proportional to the amount of dairy fat consumed.  Dairy fat contains nutrients such as vitamins A, D, K2 and healthy fats such as butyric acid, other short/medium chain fats, long chain omega 3’s, vaccenic acid and conjugated linoleic acids.  Therefore full fat dairy should be chosen to maximise health benefits when consuming dairy.

80-90 nmol/l, or even 100 nmol/l, are ideal blood levels of 25-hydroxyvitamin D for calcium absorption, as well as other health benefits.  240 µg is needed for 97.5% of the population to achieve a blood level of 100 nmol/l, although most people only need 100 µg and this depends on factors such as body weight.  The AI for vitamin D should be changed to 100 µg and an RDI should be made at 240 µg.  The recommendations regarding sun exposure should be changed to increase noon sun exposure to as much of the body as possible to promote health and not be responsible for skin cancers.

Alternatives to dairy should only include other animal foods along with an ideal blood level of 25-hydroxyvitamin D (80-90 or 100 nmol/l).  Animal-based foods are rich sources of the nutrients dairy foods are also rich in.  Many of the nutrients are only found adequately in animal-based foods and some nutrients are exclusive to animal foods.  This makes animal-based foods a better alternative to dairy than plant-based dairy substitutes.

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