Friday, April 18, 2014

Vegan, or Not Vegan? My Question About the Latest Vegan Research Report

Comparison of Nutritional Quality of the Vegan, Vegetarian, Semi-Vegetarian, Pesco-Vegetarian and Omnivorous Diet

This new study reports that Belgian people eating strictly plant-based diets have lower body mass and better overall food choices and nutrient intakes than people eating vegetarian, semi-vegetarian, pesco-vegetarian, or omnivorous diets. Those eating 'vegan' diets had diets receiving the highest scores when measured by both the USDA Healthy Eating Index and the Mediterranean Diet Index. That means that those eating plant-only diets had diets more like the Mediterranean Diet 'guidelines' than those eating any other diet category. "Vegans" consumed more than adequate protein (82 g/d on average), iron, B12, and had apparently adequate calcium intake (although calcium intake was lower than other groups).

But I found something odd in this paper that leads me to put "vegan" in scare quotes.

The researchers defined "vegan" as "not consuming any animal products" and also stated "Subjects describing themselves as vegans in the diet questionnaire, though declaring to consume animal products in the FFQ as well as reported vegetarians declaring to consume meat as indicated by the FFQ were reclassified according to their answers given in the FFQ."  This should have meant that they only included people who declared no animal product consumption, and therefore virtually no cholesterol intake, in the vegan group.

Strangely, Table 2, titled "Nutritional intake across the dietary patterns," reports that the "vegans'" consumed 149 mg cholesterol daily with a standard deviation of 92.  This appears to imply that none of the 'vegans' in this study ate a vegan diet as defined by the researchers.

Cholesterol in Plants?

Yes, plants do manufacture and utilize very small amounts of cholesterol.  According to some biochemists plants contain roughly 50 mg cholesterol per kg total lipids, i.e. 0.05 mg/g total lipids.
Cholesterol.  From Wikimedia.

In comparison, animal tissues have 5 g cholesterol per kg total lipids, or more, i.e. one hundred times more than plants.  Consequently, the amount of cholesterol in plant foods is negligible.  The richest plant sources of cholesterol are extracted plant oils.  According to Behrman and Gopalan, cottonseed, canola, and corn oils supply, respectively, 45, 53, and 55 mg cholesterol/kg total lipids.  Of interest, highly saturated coconut supplies only 14 mg/kg total lipids.  Olive oil supplies 0.5-2 and sesame oil ~1.0 mg/kg total lipids.  Of course in many whole plant foods, the absolute amount of lipids is very low resulting in very very low amounts of total cholesterol.

This study reports that the "vegans" consumed an average of 68 g total fat daily (compared to 122 g total fat among omnivores).  According to the data on plant cholesterol, that would entail a plant cholesterol intake of up to ~ 3.5 mg daily. Thus, I wonder how the researchers calculated that these "vegans" consumed an average of 149 mg cholesterol daily, roughly 40-50 times what would be expected from a strictly plant-based diet providing only 68 g total fat daily. Those with the

How much animal food would one need to consume to ingest ~ 149 mg cholesterol daily?  This is more than the amount supplied by a small whole egg (141 mg) or equal to the amount found in 240 g (roughly 8.4 ounces) of grass-fed bovine muscle meat (62 mg/100 g). 

The authors claim that they excluded from the "vegan" group anyone who reported consuming any animal products, yet also reports that the "vegan" consumed significant amounts of cholesterol potentially representing rather large amounts of animal flesh.  Their data contradicts their claimed methodology.

I can think of several possible problems.  Possibly they did not as claimed exclude from the "vegan" group people who claimed consuming animal products, therefore their "vegan" group was not actually composed of vegans.  Another possibility is this is a clerical error, but it surprises me that no one on this team of researchers nor the peer-reviewers noticed this glaring inconsistency.  It very much warrants some explanation which the authors did not provide. 

These "vegan" dieters had a lower average cholesterol intake than the other groups, but it was not low enough to convince me that they researchers only included vegans in their "vegan" group. This issue leaves me lacking full confidence in their data collection and/or tabulation.

More Data From the Study

In this study, the "vegans" consumed about 21 g saturated fat daily, omnivores, 54 g.  The vegetarian, semi-vegetarians, pesco-vegetarians, and omnivore intakes of saturated fats were 13, 14, 14, and 16 percent respectively.  Only "vegans" had a saturated fat intake less than 10 percent of calories
(8 percent), but I wonder if this data is compatible with a cholesterol intake of 149 mg/d.

Sodium intakes were also lowest among the "vegans," intermediate in the semi-vegetarian groups, and highest among the omnivores.  Plants contain far less sodium than animal tissues so this is consistent with expectations.

The "vegans" had the highest carbohydrate intake as a percent of energy (57%), and the omnivores the lowest (44%).  That is expected because plants are composed largely of carbohydrate and animal products contain little or none.  "Vegans" also had the highest intake of empty calories (solid fats, alcohol, and added sugars), 8.5% vs. 5.7% for the omnivores.

According to self-reported data, the "vegans" also had the lowest incidence of overweight (11%) and obesity (2%) while the omnivores had the highest (21% and 8%, respectively).  This data is consistent with the fact that the "vegans" had the lowest average total energy intake, and also with previous reports, such as EPIC-Oxford, which I discussed at length in Powered By Plants.

"Vegans" consumed about 23 mg iron daily, omnivores, 17 g.  This accords with other studies and also my own experience planning plant-based diets.

The "vegans" also had the lowest calcium intake, 738 mg per day, which according to recent research is about what the typical individual requires to maintain calcium balance.   However, my diet typically provides more than 2000 mg of calcium daily from plant foods, because I eat a very large amount of green leafy vegetables, fruits, nuts, and seeds rich in calcium, and also use tofu or fortified soymilk almost daily.  I think "vegans" can do better than 738 mg calcium per day with a little effort.


Although most of the reported data from this study fits expectations and accords with previous data comparing vegans, vegetarians, semi-vegetarians, pesco-vegetarians, and omnivores, I lack full confidence in the reported nutrient intakes of the "vegans" in this study because of the odd report of a substantial cholesterol intake in the "vegans."  I would like the authors to explain this portion of their data because it does not accord with the expected cholesterol content of an exclusively plant-based diet.  


Charles Grashow said...

Vegans and Vegetarians Have Higher Levels of Lifespan-Shortening AGE Products?

Charles Grashow said...

Fred Pollack said...

I emailed the 1st author, Dr. Peter Clarys, of the Belgian paper. I received a reply today:

"Thank you for your question. Indeed Vegans should not have any cholesterol... The problem is that the nutritional programs (e.g. Nubel) do not discriminate between vegan products (e.g. cookies etc not containing any cholesterol) and non vegan products. So the vegans are really vegans and the cholesterol is an artifact. Similar findings were reported by Rizzo et al. (
I will discuss with the co-authors to write an additional comment conercning your remark."