Scientific Update

A study of more than 150 German vegans provides insights into the health benefits of vegan diets as well as areas needing improvement. In this study, vegans were categorized as either strict vegans, who ate no animal products, or moderate vegans, who occasionally ate very small amounts of dairy products and eggs. Study subjects had followed a vegan diet for at least a year. Generally, diets were in accord with current recommendations and had approximately 30 percent of calories from fat, 6 percent of calories from saturated fat, and 11 percent of calories from protein. Fiber intake was quite high. Average blood lipid concentrations (total, HDL, and LDL cholesterol and triglycerides) were in the good range that is not associated with an increased risk of heart disease. Study subjects were lean and appeared very health-conscious. Only 3 percent smoked, and nearly 40 percent did not drink alcohol. Obviously, vegan diets can be health-promoting.

On the other hand, 58 percent of strict vegans and 34 percent of moderate vegans had a vitamin B₁₂ deficiency, based on the concentration of vitamin B₁₂ in their blood. They also had high concentrations of homocysteine, a substance that has been associated with an increased risk of heart disease. Elevated homocysteine can be caused by a vitamin B₁₂ deficiency. The elevated homocysteine concentrations seen in these vegans may explain why death rates from heart disease tend to be higher in vegans than in lacto-ovo vegetarians. Vegans should strive for an adequate vitamin B₁₂ intake, both to prevent vitamin B₁₂ deficiency and to reduce risk of heart disease.

Waldmann A, Koschizke JW, Leitzmann C, Hahn A. 2005.

German vegan study: Diet, life-style factors, and cardiovascular risk profile. Ann Nutr Metab 49:366-72.

Raw Food Diets Also Have Positives and Negatives

A similar study, also conducted in Germany, examined 201 participants who consumed at least 70 percent of their total food intake as raw food and who had followed this diet for at least two years. The majority of subjects ate small amounts of raw meat and fish, while approximately 20 percent were lacto-ovo vegetarians and 20 percent were vegan. More than three-quarters of the subjects ate more than 90 percent of their food in raw form. The diets of the subjects were quite low in protein with an average protein intake of 30-40 grams per day. Current recommendations call for 56 grams of protein for men and 46 grams for women. Dietary fat was around 30 percent of calories, and intakes of saturated fat were low. Blood cholesterol and LDL cholesterol concentrations were low. On the other hand, HDL (good) cholesterol concentrations were also low, with the lowest levels seen in subjects eating the greatest amounts of raw food. Close to 40 percent of participants had vitamin B₁₂ deficiency, and 50 percent had elevated homocysteine concentrations, which can be caused by a vitamin B₁₂ deficiency and has been associated with an increased risk of heart disease. Subjects who regularly used vitamin B₁₂ supplements had higher vitamin B₁₂ and lower homocysteine concentrations than subjects who did not use supplements. The low concentrations of HDL cholesterol and elevated homocysteine concentrations seen in this group following a raw food diet raise concerns about an increased risk of heart disease and stroke. It is clearly important for those following raw food diets to have adequate and reliable sources of vitamin B₁₂.

Koebnick C, Garcia AL, Dagnelie PC, et al. 2005.

Long-term consumption of a raw food diet is associated with favorable serum LDL cholesterol and triglyceride but also with elevated homocysteine and low serum HDL cholesterol in humans. J Nutr 135:2372-78.

Health Benefits of Organic Diets for Children

What would happen if only organic fruits, vegetables, and grain products were included in children’s diets? That’s what investigators in Seattle, Washington, set out to determine when they recruited 23 children aged 3-11 years for a small study. All children lived in homes where pesticides were not used. The children ate their usual diet for three days, substituted organic foods for most of their usual foods (fruits, vegetables, juices, wheat- or corn-based foods) for five days, and then ate their usual diet for seven days. The amount of organophosphorus pesticides, which are known to cause neurologic effects in humans, in the children’s urine was measured. The concentration of two of the pesticides in urine dropped below the detection limit immediately after the organic diet was started and stayed below this limit until conventional foods were reintroduced. The study authors conclude that organic diets provide protection against organophosphorus pesticide exposure in young children, especially if these pesticides are not used in the children’s homes. Foods that were most likely to contain organophosphorus pesticides included peaches, celery, sweet peppers, cherries, strawberries, wheat, barley, and soybeans. While it is not always possible to purchase organic foods, choosing organic forms of foods that are known to be most likely to contain pesticides is one way to reduce exposure to these compounds.

Lu C, Toepel K, Irish R, et al. 2006.

Organic diets significantly lower children’s dietary exposure to organophosphorus pesticides. Environ Health Perspect 114:260-63.

Protein or Monounsaturated Fats are Good Replacements for Saturated Fat

We’ve all heard that it’s important to reduce the amount of saturated fat in our diets. What’s less certain is which nutrient should replace saturated fat. Should we be eating more protein, more carbohydrate, or more unsaturated fat? A recent study tried replacing saturated fat with either protein (2/3 plant protein and 1/3 animal protein), carbohydrate, or monounsaturated fat (canola and olive oil, nuts and seeds) and then determining the effect of this on blood pressure and LDL (bad) cholesterol. Study participants were 164 adults with mildly elevated blood pressure. They were on each diet for six weeks. All diets were low in cholesterol and sodium and high in fruits and vegetables.

Blood pressure and total, LDL, and HDL cholesterol decreased on all three diets. Compared with the higher carbohydrate diet, the higher protein diet further decreased blood pressure, LDL cholesterol, and triglycerides and lowered HDL (good) cholesterol. The higher unsaturated fat diet also further decreased blood pressure and triglycerides but did not decrease LDL cholesterol. HDL cholesterol was higher on the high unsaturated fat diet. All three diets lowered the risk of heart disease, with higher protein and higher unsaturated fat diets having a greater effect than higher carbohydrates. This study suggests that, for those with high blood pressure, a somewhat higher protein intake (with at least half from plant sources) or a somewhat higher intake of unsaturated fat, along with low sodium intake and generous amounts of fruits and vegetables, can help to reduce blood pressure and may lead to lower cholesterol levels and a reduced risk of heart disease.

Appel LJ, Sacks FM, Carey VJ, et al. 2005.

Effects of protein, monounsaturated fat, and carbohydrate intake on blood pressure and serum lipids. JAMA 294:2455-64.

Flaxseed Oil Improves Blood Omega-3 Fatty Acid Concentrations

Flaxseed oil is known to be a source of alpha-linolenic acid, an omega-3 fatty acid that can be converted to another omega-3 fatty acid called eicosapentaenoic acid (EPA) and that may reduce the risk of death from heart disease. Questions have been raised about how efficiently this conversion occurs and whether people who do not eat fish (a good source of EPA) can rely on flaxseed oil and other sources of alpha-linolenic acid being converted to EPA. A recent study gave 49 African-American subjects either capsules containing 3 grams of alpha-linolenic acid from flaxseed oil or capsules containing olive oil. After 12 weeks, blood levels of EPA increased by 60 percent in the group receiving flaxseed oil but did not increase in the group receiving olive oil. This study suggests that a significant increase in blood EPA levels can occur with a relatively low dose of flaxseed oil. The researchers conclude that it is very possible to get 3 grams of alpha-linolenic acid from diet without having to use dietary supplements. Flaxseeds, canola oil, soybean oil, and walnuts are other good sources of alpha-linolenic acid.

Harper CR, Edwards MJ, DeFilipis AP, Jacobson TA. 2006.

Flaxseed oil increases the plasma concentrations of cardioprotective (n-3) fatty acids in humans. J Nutr 136:83-87.