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Low-Carb Lowdown (Part 1)

Research over the years has proven that Atkins’ assertions were correct. A low-carb diet offers cardiovascular protection. Its higher fat content raises HDL, which helps the body remove excess blood cholesterol. Lowfat, high-carb diets are known to lower HDL while raising levels of triglycerides, or blood fats. low-carb diets consistently lower triglycerides, an effect amplified when you add fish oil supplements to your diet. Low-density lipoprotein, often referred to as the bad cholesterol, because of its association with cardiovascular disease, is also favorably affected by low-carb diets. It turns out that the smaller, denser forms of LDL are more dangerous than the larger, more buoyant forms. Research shows that a low-carb diet favors the formation of the larger, benign LDL molecules.3 That’s why the low-carb diet is now suggested as an effective form of therapy to treat the metabolic syndrome, a harbinger of cardiovascular disease and diabetes.

A recent study of guinea pigs, which process cholesterol much as humans do, revealed one way that low-carbohydrate diets help control cholesterol. A high intake of dietary cholesterol increases the activity of an enzyme in the liver that synthesizes fat. But when the guinea pigs are put on low-carb diets, the enzyme is suppressed, despite a high amount of cholesterol in the animals’ diets.4 Another recent animal study found that a high-fat, low-carb diet helps prevent the enlarged heart associated with high blood pressure.5

Human studies likewise confirm the beneficial effects of low-carb dieting. One example is a recent study involving moderately obese human subjects who followed two types of low-carb diets. One featured foods high in saturated fat, such as meat, similar to what Dr. Atkins originally suggested. The other diet focused on fish, poultry and shellfish that contained a high content of polyunsaturated fats, which are suggested for reducing elevated blood cholesterol. After 28 days both diets proved equally effective in stimulating weight loss, and neither diet adversely affected blood cholesterol, although the diet that had more polyunsatured fat more effectively lowered triglycerides.6

While some saturated fatty acids, such as palmitic acid, can increase cholesterol, they don’t do so in the presence of polyunsaturated fatty acids, such as linoleic acid, found in vegetable oils and food. The authors observe that fears of soaring cholesterol from eating low-carb diets don’t make biological sense. Saturated fats are most potent in increasing HDL, while polyunsaturated are the least efficient.

Another study found that eating a low-carb diet seemed to trigger selective bodyfat loss. Seventy percent of the subjects, who were all men, lost more fat on a low-carb diet, even though they ate more calories. They also lost more fat in the chest and stomach—highly significant because fat stored in those areas is more metabolically active and is linked to cardiovascular disease, high blood pressure, diabetes and the metabolic syndrome. In fact, they lost three times as much fat in the trunk area as those on a lowfat diet.7

While a diet high in cholesterol and saturated fat is often linked to the onset of Alzheimer’s disease, that correlation may not be correct. A recent animal study found that a low-carb diet lowered a protein that accumulates in the brains of those with Alzheimer’s disease and is considered a major cause of the disease.8 That makes sense because a protein in the brain called insulin-degrading enzyme is known to break down both beta-amyloid, the toxic protein in Alzheimer’s, and insulin. Eating too much carbohydrate increases insulin. That makes the insulin-degrading enzyme focus on insulin, enabling excess beta-amyloid to accumulate in the brain, which has led many researchers to refer to Alzheimer’s as “type 3 diabetes.”

Recent animal studies also show that low-carb diets, by lowering both insulin and insulinlike growth factor 1, may prevent prostate cancer.9 In contrast, diets high in refined carbs are linked to prostate cancer.10

So are low-carb diets dead? Apparently not for those who want to live longer. In Part 2 we’ll discuss why low-carb diets are effective. IM

1 Bravata, D.M., et al. (2003). Efficacy and safety of low-carbohydrate diets. NEJM. 289:1837-1850.
2 Foster, G.D., et al. (2003). A randomized trial of a low-carbohydrate diet for obesity. NEJM. 348:2082-2090.
3 Sharman, M.J., et al. (2004). Very-low-carbohydrate and lowfat diets affect fasting lipids and postprandial lipemia differently in overweight men. J Nutr. 134:880-885.
4 Torres-Gonzalez, M., et al. (2007). Carbohydrate restriction alters hepatic cholesterol metabolism in guinea pigs fed a hypercholesterolemic diet. J Nutr. 137:2219-2223.
5 Okere, I.C., et al. (2006). Low carbohydrate/high fat diet attenuates cardiac hypertrophy, remodeling, and altered gene expression in hypertension. Hypertension. 48:1116-1123.
6 Cassady, B.A., et al. (2007). Effects of low-carbohydrate diets high in red meats or poultry, fish, and shellfish on plasma lipids and weight loss. Nutr Metab. 4:23.
7 Volek, J.S., et al. (2004). Comparison of energy-restricted very-low-carbohydrate and lowfat diets on weight-loss and body composition in overweight men and women. Nutr Metab. 1:12.
8 Van der Auwera, I., et al. (2005). A ketogenic diet reduces amyloid beta 40 and 42 in a mouse model of Alzheimer’s disease. Nutr Metab. 2:28.
9 Freedland, S.J., et al. (2007). Carbohydrate restriction, prostate cancer growth, and the insulin-like growth factor axis. The Prostate. In press.
10 Venkateswaran, V., et al. (2007). Association of diet-induced hyperinsulinemia with accelerated growth of prostate cancer (LNCaP) xenografts. JNCI. 99:1793-1800. IM

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