Tuesday, August 27, 2013

What Can Our Nutrient Requirements Tell Us About Diet?

We can infer some of the foods/dietary patterns we are better adapted to by using evolution in the context of our nutrient requirements 

* Just so people are aware this blog post isn’t about the optimal amount/ratio/whatever of a given nutrient or food.  Please don’t take ‘required amount’ to mean ‘optimal amount’ (and in what context?) 

An Omnivorous Diet 

Not all of the recommended daily intakes are based on requirements or on ‘optimal’ amounts.  Even so, they can be a good guide as to what we need.  One of the purposes behind doing my nutrient database was to look at which nutrients various food groups were good and poor sources of.  One thing I found was that animal foods tend to rich sources of some nutrients and plant foods tend to be rich sources of other nutrients, which suggests we should eat both animal and plant foods.  As an omnivorous species, this shouldn’t be particularly surprising. 

Vitamins and Minerals
Animal but not Plant Foods
Plant but not Animal Foods
Zinc*
Calcium
Selenium*
Potassium
Riboflavin
Copper*
Niacin
Manganese*
Vitamin B5
Vitamin C*
Vitamin B6
Thiamine
Biotin
Folate*
Choline*
Vitamin E*
Vitamin B12*
Vitamin K1
Vitamin K2*
Other Nutrients
Animal but not Plant Foods
Plant but not Animal Foods
Carnitine, Carnosine, Creatine, Taurine
Phenolic Compounds
Long Chain Omega 3 Fatty Acids*
Carotenoids
Conjugated Linoleic Acids
Soluble Fibre
Coenzyme Q10

* The nutrients with an asterisk are those that carnivores or vegans would most likely or certainly become deficient in 

Calcium

The RDI for calcium is 1,000 mg per day, which was based on calcium balance experiments that found calcium balance occurs at 840 mg.  The most common way of meeting the 1,000 mg per day target is through dairy consumption.  Yet, given the lack of dairy throughout evolution the idea that we need dairy for calcium is a bit absurd.  Rather than a biological need for dairy there might be other explanations for the high calcium requirement: 

  • Historically other high calcium foods may have been eaten such as fish bones, the bones of small animals, more calcium-rich plants, etc
  • Plant foods probably used to be higher in nutrients like calcium [1]
  • The subjects in those calcium balance studies probably had lower than ideal levels of vitamin D and K2 (given sun and SFA/cholesterol phobia) 

Choline 

The adequate intake for choline in men is 550 mg.  This is based on an amount of choline that didn’t increase ALT levels (500 mg), +10% [2] [3].  Like calcium, we seem to have a pretty high requirement for choline that is quite difficult to meet without the inclusion of certain foods.  Non-starchy vegetables, meat, shellfish, organ meats, eggs and wheat are pretty much the only good sources of choline.  Although you need a lot of non-starchy vegetables, meat or shellfish for 550 mg of choline. 

Food
Amount of Food to Needed for 550 mg of Choline
Non-starchy vegetables
Few kgs of vegetables (depending on which ones)
Spinach
450g
Meat
~200g of protein (~1kg of meat)
Shellfish
Roughly several hundred grams
Wheat
8.5 slices (240g) of whole wheat bread [4] [5]
Beef Liver
160g
Eggs
220g (~3 eggs)

With most other food sources being pretty poor sources (<50%) or barely/nearly adequate (low fat dairy and legumes).  I would guess that historically the major source of choline was organ meats such as liver, seeing as the sheer quantity of vegetables is unrealistic, eggs would have been smaller and an unreliable source and wheat used to only be found in NE Africa and the Middle East 

Non-Essential Amino Acids 

In Beyond Good and Evil, Chris Masterjohn discusses how many diets are low/deficient in glycine and the need to balance glycine and methionine to prevent excess methylation and promote adequate glutathione synthesis.  Good glycine sources are skin and bones 

Creatine is tri-peptide found in meat and can be synthesised using arginine, glycine and methionine.  Even though we can synthesise creatine vegetarians have lower levels of creatine [6], which seems to negatively affect their memory (as creatine improved memory in the vegetarians but not the meat eaters) [7].  Vegetarians have lower levels of some other non-essential amino acids (carnitine [6], carnosine (vegetarians have more AGEs and carnosine inhibits formation of AGEs, but other factors could be involved) [8] and taurine (vegans) [9]) and those nutrients are beneficial, although at this time no studies suggest vegetarians are worse off because of their lower levels (like ref 7) 

Carbohydrate 

Carbohydrates aren’t technically an essential nutrient, but outside of ketosis it kind of is in practice.  Most of our carbohydrate needs aren’t genetically determined (unlike the stuff in this post) but rather are largely determined by our brain’s need for glucose.  The US DRI has set an EAR of 100g and an RDA of 130g of carbohydrate per day to cover our basic glucose needs [10] 

In Perfect Health Diet (PHD) the Jaminets find 150-480 glucose calories are required for the central nervous system (150 only when offset by ketones), 200-300 for glycoproteins and 100 for other uses, which comes to 780-880 *.  Fat in food comes in the form of triglycerides.  The glycerol in triglycerides can be converted to glucose, so some of the glucose calories can be met through fat.  The amount of glycerol can be determined by the percentage of glycerol calories in triglycerides (12%) multiplied by the total fat calories in the diet.  A 2,400 calorie PHD provides 187.2 glucose calories from glycerol, reducing the glucose needs to 600-700 calories or 25-29% of total calories (outside of gluconeogenesis from amino acids, which doesn’t contribute much anyway) [11]. 

* The need will be higher with intense exercise 

Long Chain Omega 3’s 

There’s lots of talk about the benefits of omega 3s, but not all omega 3s are equal.  In order to have much effect the shorter chain omega 3s like ALA (18:3) need to have more double bonds (desaturation) and become longer (elongation) to EPA (20:5) and DHA (22:6) and then get incorporated into cell membranes and form eicosanoids or docosanoids 

The conversion rate of ALA to EPA and especially DHA is extremely poor.  One review suggests ~5% of ALA is converted to EPA and only <0.5% of ALA is converted to DHA.  For this reason large amounts of ALA have a negligible impact on plasma DHA levels [12] 

ALA is mainly found in plants and plant oils while EPA and DHA are almost exclusively found in animal foods (algae contains DHA).  Healthy vegans have lower plasma DHA, but have no symptoms of DHA deficiency * [12]. 

* It’s suggested that vegans must be synthesising more DHA and/or reducing DHA turnover.  However, the plasma level of DHA doesn’t increase much with ALA supplementation [12]. 

Summary 

Our genetics and physiology suggest we should be better adapted to an omnivorous diet that includes at least meats, organ meats, skin, >25-30% of total calories from carbohydrate and perhaps bone or calcium rich plants. 

(I realise this post was quite meat/animal food focussed, which wasn’t my intention.  I actually planned to have a section on vitamin C, but I realised our very low ‘requirement’ tells us very little as it can be met with a piece or two of fruit) 

Further Reading:
(1) Meeting the Choline Requirement -- Eggs, Organs, and the Wheat Paradox
(2) Beyond Good and Evil
(3) Extremely Limited Synthesis of Long Chain Polyunsaturates in Adults: Implications for their Dietary Essentiality and use as Supplements

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