Warning: Lots of biochemistry discussed below. Hopefully the general ideas of the article will make sense even if you skim over the more technical parts.
A study just came out with a scary title, “Vegetarianism produces subclinical malnutrition, hyperhomocysteinemia and atherogenesis.” The abstract shows that the cross-sectional study measured homocysteine levels (among other disease markers) of a rural population of men living in Chad who were supposedly vegetarian (1). They found homocysteine levels to be elevated and therefore concluded that the men might be at risk for cardiovascular disease. Except for the provocative title, there was nothing particularly interesting in the abstract, and I decided not to pursue it further as there is a steady flow of cross-sectional studies on semi-vegetarians from developed countries and their cardiovascular disease markers.
But a number of people contacted me about it and so I changed my mind. I’m glad I did, as the paper was much more interesting than the abstract, though still not very relevant to vegetarians in developed countries.
Here is a summary. Twenty-four apparently healthy men from a rural part of Chad, a country in Africa, were compared to 15 men from a nearby urban part of Chad. The rural men ate very little animal products and less than their urban counterparts. There is no indication that this was due to any sort of “vegetarianism,” but rather simply because of the food available to them in their area.
Protein intakes for the rural men were an average of 50 g per day compared to 63 g per day for the urban men. The RDA for meat-eating men of that height would be 51 g and the recommended protein intake for vegan men that height would be 57 g. That would put these rural men at a “probably adequate” protein level, in my opinion. However, their average intake of the sulfur amino acids methionine and cysteine was only 10.4 mg/kg while the RDA is 19 mg/kg.
The rural men were marginally suffering from an indicator of protein malnutrition, known as prealbumin (aka as transthyretin), which was at an average level of 176 mg/l (compared to 292 mg/l for the urban men). The lower limit of a healthy prealbumin is listed by most sources as 180 mg/l, while the upper limit of healthy is listed as anywhere from 300 to 400 mg/l.
The B12 levels of the rural vs. urban men were 174 vs. 269 pmol/l. Homocysteine levels of the rural vs. urban men were 19 vs. 11 µmol/l.
Some background: Homocysteine is a byproduct of methionine metabolism and is considered to be a risk factor for heart disease and stroke (among other diseases). Generally, homocysteine is raised by either vitamin B12, folate, or vitamin B6 deficiency. Vegetarians and vegans who do not supplement with vitamin B12 typically have elevated homocysteine levels. A level of 8 µmol/l or below is ideal, whereas greater than about 12 µmol/l is associated with increased risk of disease.
In the past, some people have thought that elevated homocysteine was caused by high levels of methionine in the diet, although this was put to rest some years ago.
Now, here is the interesting part of this study (if you happen to find the folate/methionine cycle interesting). Because the rural men were not technically deficient in vitamin B12, but were marginally protein malnourished, the researchers thought it was not vitamin B12 deficiency that was causing the elevated homocysteine but rather marginal intakes of the amino acid methionine. Their theory is that when you are deficient in methionine, the body produces excess homocysteine from cysteine so that it can then create methionine and, in turn, s-adenosylmethionine (SAMe) which is an important methyl donor for many reactions throughout the body.
My take on this is somewhat different. Although the vitamin B12 levels in the rural men were technically not in the deficiency range, they were not ideal for homocysteine levels. Selhub (2) suggests a minimum vitamin B12 level of 300 pmol/l for minimizing homocysteine levels and this is born out in the current study in that even the urban men with a B12 level of 269 pmol/l had a slightly elevated homocysteine of 10.8 µmol/l while getting plenty of protein.
Despite the title of the study saying that vegetarianism produces atherogenesis, there was no mention of this in the paper. In fact, the cholesterol levels of the rural and urban men were at relatively low levels of 154 and 166 mg/dl respectively (which is not a direct measure of atherogenesis, but low cholesterol levels are often associated with low atherogenesis).
A press release published in SFGate.com did a write-up on the study (which is what caught some people’s attention): Vegetarian Diet Might Increase the Risk of Cardiovascular Diseases, According to a Recent Study, Says Nutri-Med Logic Corp. While I would not describe their release as terribly inaccurate, they fail to mention that the study was of semi-vegetarians in Chad who were arguably malnourished. Their suggestion of supplementing with alpha-lipoic acid to combat what is either B12 or protein malnutrition is a stretch.
The take home message from this study is: People who limit animal product consumption need a regular source of vitamin B12. People who follow a vegetarian diet due to a lack of food in an area with low amounts of available plant protein could become protein malnourished and this could possibly exacerbate elevated homocysteine levels. Vegans in developed countries can easily avoid these problems by supplementing with vitamin B12 and getting enough protein.
1. Ingenbleek Y, McCully KS. Vegetarianism produces subclinical malnutrition, hyperhomocysteinemia and atherogenesis. Nutrition. 2011 Aug 26. [Epub ahead of print] Link
2. Selhub J, Jacques PF, Dallal G, Choumenkovitch S, Rogers G. The use of blood concentrations of vitamins and their respective functional indicators to define folate and vitamin B12 status. Food Nutr Bull. 2008 Jun;29(2 Suppl):S67-73. Review. Link