Scientific Update
By Reed Mangels, PhD, RD
Red Meat or White Meat? How About NO Meat?
A study which was funded by the National Cattlemen's Beef Association examined the
effects of using lean red meat (beef, pork, and veal) compared to lean white meat
(poultry and fish) on blood cholesterol levels. Subjects had high cholesterol levels
to begin with. The 191 study subjects ate 6 ounces of meat 5 to 7 days a week, with
the meat either mainly lean white or lean red, depending on the group to which they
were assigned. Subjects followed this diet, which had less than 30% of calories from
fat and less than 300 milligrams of dietary cholesterol, for 36 weeks. The
researchers found that white meat is not the only way to lower blood cholesterol
levels. They found approximately a 1% reduction in cholesterol in the red meat group
and a 1.8% reduction in the white meat group.
Now, let's suppose we placed the subjects on a vegetarian diet. One study which did this in people whose cholesterol levels were already within normal range found that they still had a 13% decrease in total cholesterol (Atherosclerosis 1982; 44: 293-305). Another study found that when people with heart disease (I am guessing they had high cholesterol) were placed on a vegetarian diet, cholesterol decreased 10% (NEJM 1985; 312: 805-811). It seems to me that a 10 or 13% reduction in cholesterol is a lot better than a 1% drop. Red meat or white meat? I'd go veggie!
Davidson MH, Hunninghake D, Maki KC, et al. 1999. Comparison of the effects of lean red meat vs lean white meat on serum lipid levels among free-living persons with hypercholesterol-emia. Arch Intern Med 159: 1331-1338.
Meat: Not a Great Source of Vitamin B-12?
Meat has long been praised as an excellent source of vitamin B-12. Recent findings
raise questions about how well vitamin B-12 is absorbed from meat and whether or not
meat can be said to be a "good" source of vitamin B-12. Close to 3,000 adults from
Framingham, Massachusetts were studied to see what their blood vitamin B-12 levels
were and what sources of vitamin B-12 they used. Those subjects who took vitamin
B-12 supplements were less likely to have low blood vitamin B-12 levels, suggesting
that vitamin B-12 is well absorbed from supplements. Those subjects who got
approximately 6 micrograms of vitamin B-12 daily from supplements (the usual dose in
a multi-vitamin) had blood vitamin B-12 levels which were similar to those who used
higher doses of vitamin B-12. This suggests that there is no advantage to regular
use of higher doses of vitamin B-12 for the healthy adult population. Use of vitamin
B-12-fortified cereals and cow's milk also seemed to protect against low blood
levels of vitamin B-12. Meat did not appear to be protective. The group who had the
highest intake of vitamin B-12 from meat consumed almost 3 times more vitamin B-12
than did the group consuming the lowest amount of meat, but there was little
difference in the number of subjects with sub-normal blood vitamin B-12 levels among
the groups. Apparently, vitamin B-12 is better absorbed from supplements, fortified
breakfast cereals, and dairy products than from meat, poultry, and fish.
Tucker KL, Rolls S, Rosenberg I, et al. 2000. Plasma vitamin B-12 concentrations relate to intake source in the Framingham Offspring Study. Am J Clin Nutr 71: 514-522.
The Effect of a Lacto-ovo Vegetarian Diet on Weight Training
As we get older, we typically lose muscle and gain fat. This, in turn, increases our
risk of developing high blood pressure, diabetes, heart disease, obesity, and
osteoporosis, and may also contribute to lower activity and increased frailty.
Strength training (lifting weights) by older people has been promoted to reduce the
risk of these problems.
Is diet important during strength training? To examine this, 19 men aged 51-69 were placed on either a non-vegetarian or a lacto-ovo vegetarian diet for 12 weeks, during which they began a strength training regimen. The men on the non-vegetarian diet had increased muscle mass and decreased fat while the men on the lacto-ovo vegetarian diet had a decrease in muscle mass and an increase in fat. Strength increased in both groups. Differences between the groups were apparently not due to differences in the amount of dietary protein; they may have been due to changes in hormone levels. Certainly, a change in both diet and exercise may lead to different results than changing only one of these variables. We can only wonder if results would have been the same if long-term vegetarians and non-vegetarians had each begun weight training with neither group making dietary changes. It is also not clear from this study what the effect of a vegan diet on the response to weight training would be.
Campbell WW, Barton ML Jr, Cyr-Campbell D, et al. 1999. Effects of an omnivorous diet compared with a lacto ovovegetarian diet on resistance-training-induced changes in body composition and skeletal muscle in older men. Am J Clin Nutr 70: 1032-1039.
Iodine in Vegetarian Diets
Iodine is a part of the thyroid hormones. Iodine deficiency leads to a variety of
problems ranging from a slight enlargement of the thyroid gland to mental
retardation. Table salt fortified with iodine is a major source for many people in
the US. Some have expressed concern about the iodine intake of vegetarians since
common food sources such as seafood and possibly dairy products are avoided and
because vegetarians may choose to not use iodized salt. Iodine content in plants is
quite variable depending on soil content and other factors.
Two recent studies have examined iodine status and intake in vegetarians. Remer and colleagues fed 6 volunteers a diet consisting mainly of fruits, vegetables, and dairy products; a non-vegetarian diet; and a diet high in meat and dairy products. None of the subjects ate fish, iodized salt, or processed foods. The subjects' iodine intake was lowest when they were on the vegetarian diet (since there were few dietary sources of iodine). However, regardless of diet, subjects had iodine intakes below recommendations. An invited commentary in the same issue of the journal which published this study (Davidsson, 1999) points out that both vegetarian and non-vegetarian diets can be low in iodine if they exclude iodized salt and other rich sources of iodine. Lightowler and Davies examined iodine intake and status of 30 vegans. Iodine intake was variable but more than 1/3 of men and more than 60% of women had iodine intakes below the recommended level. Apparently the subjects did not use iodized salt. Certainly further study is needed to determine if these low levels of iodine intake had harmful effects on thyroid function.
These studies suggest that vegetarians (and non-vegetarians) should use iodized salt or other reliable sources of iodine.
Remer T, Neubert A, Manz F. 1999. Increased risk of iodine deficiency with vegetarian nutrition. Br J Nutr 81: 45-49.
Lightowler HJ, Davies GJ. 1999. Iodine intake and iodine deficiency in vegans as assessed by the duplicate-portion technique and urinary iodine excretion. Br J Nutr 81: 529-535.
Davidsson L. 1999. Are vegetarians an 'at risk group' for iodine deficiency? Br J Nutr 81: 3-4.
Rheumatoid Arthritis: Dietary Influences?
We don't know what causes rheumatoid arthritis, a painful condition which affects
the joints. Diet is one factor which has been proposed to affect the development of
this condition. Researchers from the US and Greece examined dietary factors and risk
of rheumatoid arthritis in Greece. Use of greater amounts of cooked vegetables and
olive oil throughout life appeared to reduce risk of developing rheumatoid
arthritis. Researchers were unable to identify what it was about these foods which
was protective, but they theorized that cooking vegetables helps the body absorb
more of some substance which helps prevent rheumatoid arthritis. The type of fatty
acids in olive oil may explain its effect.
Linos A, Kaklamani VG, Kaklamani E, et al. 1999. Dietary factors in relation to rheumatoid arthritis: a role for olive oil and cooked vegetables? Am J Clin Nutr 70: 1077-1082.
Diet and Skin Cancer
Skin cancer (basal cell carcinoma type) is thought to be caused in part by sun
exposure. Other factors, including diet, may also increase risk. Researchers
examined more that 43,000 men, more than 3,000 of whom were diagnosed with basal
cell carcinoma. Higher intakes of fat, especially monounsaturated fat (like olive
oil) were associated with a slightly reduced risk of developing basal cell
carcinoma. Saturated fat and polyunsaturated fat appeared to have little effect.
Higher intakes of folate (a vitamin found especially in green leafy vegetables and
in fortified foods) appeared to slightly increase risk. Carotenoids and vitamins A,
C, D, and E did not appear to have a protective effect. The results of this study
suggest that diet has little effect on the development of basal cell carcinoma in
men.
van Dam RM, Huang Z, Giovannucci E, et al. 2000. Diet and basal cell carcinoma of the skin in a prospective cohort of men. Am J Clin Nutr 71: 135-141.
