Sunday, February 12, 2012

DGA 2011 - Meat, Eggs and Alternatives

2.4 Lean meat and poultry, fish, eggs, nuts and seeds, and legumes/beans

Animal-Based vs Plant-Based Nutrition

“The ‘lean meat and alternatives’ food group is diverse, both nutritionally and biologically. The foods in this group have traditionally been seen as ‘protein-rich’, but they also provide a wide variety of other nutrients which may be more important in the typical high-protein Australian diet.”

Just like the section on dairy, this food group has been reduced to being protein-rich.  The so called ‘high protein Australian diet’ is where energy derived from protein comes to about 16.7% of total energy [1], which is towards the lower limit of the optimal protein range (15-25% of total calories) to lower chronic disease risk [2].

Seeing as one of the main nutrients of this group is protein it would be a good idea to make sure these foods are rich in protein and their protein is high quality.  Most nuts contain less than 10% of protein as total calories, which is below the RDI for protein.  Almost all nuts and seeds (except for pumpkin seeds and perhaps a few others) contain less than 15% of protein as total calories, which puts them below the optimal protein range to lower chronic disease risk [3].  With this information nuts and seeds already don’t belong in the category of protein-rich foods and should therefore not be considered a good source of protein (because technically all foods are a source of protein or ‘protein source’).

A common practice in vegetarian circles is to combine lysine poor grains with methionine and cysteine poor legumes.  This results in a less unbalanced meal.

Methionine and cysteine are used to synthesise other compounds that have many health benefits, so replacing meat with legumes will likely decrease the synthesis of these compounds.  Methionine or lysine can be used to synthesise carnitine.  Carnitine lowers triglycerides and increases fat metabolism by transporting fatty acids into the cell [4], decreases oxidised LDL [5] and increases mitochondrial biogenesis when used with lipoic acid [6].  Methionine, arginine and glycine can be used to synthesise creatine.  Creatine is used in the anaerobic creatine phosphate energy system, can improve exercise performance, increase muscle mass [7] and improves cognition [8].  Cysteine, glutamic acid and glycine can be used to synthesise glutathione, sometimes called ‘the master antioxidant of the cell’.  (Cysteine is the rate limiting amino acid in glutathione synthesis [9]).  Glutathione is needed to form glutathione peroxidase and glutathione transferase, enzymes used in reducing free radicals and detoxification.  Cysteine can be used to synthesise taurine, which has a number of functions and health benefits such as reducing insulin resistance [10], triglycerides and ApoB (a marker for LDL and VLDL particles) [11].

Histidine and alanine can be used to synthesise carnosine, which buffers acidity, increases athletic performance [12], blocks protein glycation and chelates heavy metals [13].

Carnitine, carnosine, creatine, glutathione and taurine are synthesised from amino acids, so I will call them collectively the ‘amino acid derivatives’.  In addition to being a good source of the required amino acids, animal foods are rich in the amino acid derivatives as preformed nutrients (carnitine [14]) (carnosine [15]) (creatine [16]) (taurine [17]).  Due to not eating meat, vegetarians and vegans have lower levels of these nutrients in their body (carnitine [18] [19]) (carnosine [15]), (creatine [16]), (taurine [20]).  Glutathione is also found in fruits and vegetables [21] and provided vegetarians consume enough protein (read: methionine and cysteine) they are likely to have sufficient levels [22].

Although data for the concentration of the amino acid derivatives in food is hard to come by, their functions can give us a rough indication.  In addition to all the health benefits above, carnitine (when used with lipoic acid) [23], carnosine [24], creatine [25] and taurine [26] [27] are antioxidants found in mitochondria and also support mitochondrial function.  Mitochondria are responsible for generating most of the ATP.  Energy production tends to be highest in the brain, liver, heart and skeletal muscle, so these tissues are likely to have many mitochondria, therefore the amino acid derivatives are likely to be found richly in foods originating from those body parts.  This is consistent with the limited data available when their other functions are also considered (for example taurine and kidney function).  Plant foods are likely not good sources of these nutrients because plants produce much less energy than animals, hence fewer mitochondria.  The same can be said for other mitochondrial antioxidants such as coenzyme Q10, which also has an essential role in the electron transport chain.  CoQ10 is found mostly in organ meats, muscle meat and some vegetable oils [28].

When considering the value of nutrients, those that are essential and those that the body manufactures are likely to be more important.  The amino acid derivatives are highly valued nutrients as they are roughly half sourced from diet and half from synthesis.  It’s possible to have a deficiency in those kinds of nutrients.  For example, glutathione deficiency is followed by mitochondrial damage [29], which can lead to neurodegenerative disorders such as Parkinson’s disease [30].  Another example is that statin drugs inhibit CoQ10 synthesis, so unless additional CoQ10 is consumed to compensate statins can cause a CoQ10 deficiency, which can lead to mitochondrial dysfunction and type 2 diabetes [31].  On the other hand phytochemicals are neither essential nor manufactured, and there’s no such thing as a polyphenol deficiency.  Instead polyphenols (a large group of phytochemicals) are often antipredation mechanisms and mildly toxic, but we gain some benefits from them through a hormetic response that up regulates our own antioxidant activity to protect against the oxidative potential of polyphenol [32].  The guidelines seem to be biased in favour of plant foods as they discuss phytochemicals thoroughly but neglect to mention the amino acid derivatives and CoQ10.

Protein is widely considered to be healthy, yet our healthy protein intake limited to 15-25% of total calories due to potential ammonia excretion [2].  Seeing as we are limited in our protein intake we should aim to maximise protein quality.  Animal protein is more bioavailable, has optimal amino acid ratios and is a rich source of the amino acid derivatives.  Therefore animal protein should make up as much of the protein calories as possible and plant protein should be considered poor sources of quality protein.

“Important nutrients include iodine, iron, zinc, vitamins, especially B12, and essential fatty acids including long chain omega-3 fatty acids.”

“Nuts and seeds are rich in energy (kilojoules) and nutrients, reflective of their biological role in nourishing plant embryos to develop into plants. In addition to protein and dietary fibre, they contain significant levels of unsaturated fat, although this varies within the category. Nuts are also rich in polyphenols and micronutrients, including folate, several valuable forms of vitamin E, selenium, magnesium and other minerals.”

“Legumes/beans, including lentils, tofu and tempe, provide a valuable and cost efficient source of protein, iron, some essential fatty acids, soluble and insoluble dietary fibre and micronutrients.”

Not only are plant foods poor alternatives to animal food in terms of protein quality, but also in micronutrients.

Nuts and seeds are not rich sources of folate and nuts are not a rich source of selenium [3].  (Brazil nuts are very rich in selenium, 1 nut provides more than the RDI).  Nuts and seeds require vitamin E as it is quickly depleted to protect their high quantities of delicate PUFA from lipid peroxidation [33].  Many minerals in nuts and seeds have reduced bioavailability, but they are still likely to be good sources of many minerals.  Mature legumes are mediocre sources of micronutrients and poor sources of most vitamins.  See the response to section 1.1.

The essential fatty acids in legumes, nuts and seeds are either from linoleic acid or alpha-linolenic acid.  They contain none of the highly sought after long chain omega 3s.  The PUFA in most nuts and seeds is almost exclusively linoleic acid.  Most legumes are also high in linoleic acid and have a high omega 6:3 ratio, including soy, which is about 8:1 [3].  High linoleic acid diets are also associated with insulin resistance and cancer [34] and the resulting high omega 6:3 ratio is pro-inflammatory and associated with poor health outcomes [35].  The alpha-linolenic acid in these foods (especially flaxseeds and walnuts) isn’t very helpful.  It is so poorly converted to DHA that DHA should be considered an essential nutrient.  This is reflective of our ancient diets, rich in wild/grass-fed meat and fish [36].

Legumes, nuts and seeds are not good alternatives to meats because they don’t share many of the same nutrients such as vitamin B12, long chain omega-3 fatty acids and the amino acid derivatives (previously discussed) [3].  There are more nutrients that animal foods are rich in, but most plant foods aren’t.  These include zinc, selenium, riboflavin, niacin, vitamin B5 [3], vitamin B6 (due to poor absorption of plant forms [37]), biotin [38], choline [3], vitamin K2 [39], conjugated linoleic acids (found only in food from ruminants and perhaps eggs) [3], coenzyme q10 [28].  Plant foods are also rich in several nutrients that most animal foods tend to be low in.  Below is a table to show the nutrients animal foods tend to be rich that plant foods tend not to be rich in and vice versa.

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
Amino Acid Derivatives
Phenolic Compounds
Long Chain Omega 3 Fatty Acids
Carotenoids
Conjugated Linoleic Acids
Lauric Acid
Coenzyme Q10
Soluble Fibre

As omnivores, to be well nourished we need a diverse range of nutrients, sourced from both animal and plant foods.  It is common that animal foods are rich in a nutrient that plant foods are low in and vice versa.  Therefore the only alternatives to an animal food should be other animal foods, and likewise the only alternatives to a plant food should be other plant foods.

Animal Food Consumption in Studies – Definitions and Confounding

Despite meats being good sources of a number of animal-source nutrients, the dietary guidelines cites research suggesting meats are associated with an increased risk of some diseases.  What’s interesting is that meats are positively associated with cardiovascular disease, but dairy is negatively associated cardiovascular disease.  One of the proposed mechanisms by which dairy reduces cardiovascular disease is increased HDL-C, yet meats will also increase HDL-C.  Dairy and meats also have a similar nutrient profile: both are rich in vitamin K2, saturated fat as well as other nutrients less related to cardiovascular disease.  In section 3.1 the guidelines have said saturated fat increases risk factors for heart disease, but dairy has a greater proportion of saturated fat compared to meats.  It would be logical to think that with similar nutrient profiles these foods will exert similar effects, but that is not the outcome of epidemiological evidence.

“The evidence is difficult to interpret because of widely varying definitions of ‘meat’. Some studies include only unprocessed red meat. Others may include some or all of a variety of processed meats, including smoked, salted and chemically preserved foods, with meat within dishes such as pizza, lasagna or casseroles variously included or excluded.”

This poses a problem.  Meats are often grouped with processed meat and are often found is foods like pizza.  When we find poor health outcomes associated with pizza is it meat is the pizza, which only makes up a small part?  Or is it the white flour, the hydrogenated or deodorised vegetable oils and the chips and sugary drinks that pizza is paired with?

“As with other areas of diet and disease risk, an individual’s dietary pattern may be more relevant than a direct effect from a single component”

With guidelines such as these suggesting meats increase the risk of some disease and that plant-based foods are suitable alternatives, it’s not surprising that some people consider meats to be unhealthy.  Some health conscious people become vegetarian for that reason.  Some studies find data that suggests vegetarians live longer [40], but this is heavily confounded by health conscious people becoming vegetarians and eating more whole, unprocessed food [41].  Similarly, intervention trials based on Mediterranean diets may reduce red meat, but also emphasise whole, unprocessed food.  Multifactorial interventions such as Mediterranean diets cannot be used to draw conclusions about the health outcomes from any one food or nutrient.  The only conclusion that can be drawn is that the intervention improves health outcomes compared to the control group.  Once again, does removing meats from the diet improve health?  Or is this confounded by reducing processed and junk foods, thereby improving food quality in the diet?  This is supported by health conscious omnivores having similar rates of mortality than pragmatic vegetarians (health conscious people who decide to become vegetarian), and that pragmatic vegetarians are healthier than ideological vegetarians (removing meats for political or ethical reasons) [42].

Conclusion

Animal protein is superior to plant protein because of its high bioavailability, optimal amino acid ratios and the presence of amino acid derivatives.  Animal foods are rich in several nutrients plant foods are low in and vice versa.  Some of these nutrients are fat soluble, such as long chain omega 3’s, conjugated linoleic acids, coenzyme Q10 and vitamins A and K2.  Animal fats tend to be high in chemically stable SFA and MUFA, and low in the highly reactive PUFAs (see response to section 3.1).  So in order to consume a nourishing and low oxidative stress diet – animal protein and fat should make up most of the total protein and fat consumed.

Meats have been associated with poor health outcomes, but this may be due to other factors.  The guidelines express the limitations of the data by acknowledging the how various definitions of meat may combine red and processed meat, how unhealthy foods used to measure meat consumption and how health conscious people restricting meat is a strong confounding variable in epidemiology.

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