Healthnotes Newswire — Adding walnuts to the diet can help normalize cholesterol without promoting weight gain, according to a study published in last month’s edition of the American Journal of Clinical Nutrition.¹ These findings are consistent with population studies that have shown eating 142 grams (about 5 ounces) of nuts per week is associated with a 30–50% decrease in coronary heart disease,^{2 3 4 5 6} America’s number one killer.

In the small clinical trial, participants followed a sequence of four different diets: (1) their habitual diet (HD); (2) their habitual diets plus walnuts (HD W); (3) a low-fat diet (20% fat; LFD); and (4) a low-fat diet plus walnuts (LFD W). The amount of walnuts consumed was approximately 48 grams (about 1.7 ounces) per day. The HD lasted four weeks, and each subsequent phase of the trial lasted six weeks, for a total duration of five and one-half months.

Both total cholesterol levels and LDL (“bad”) cholesterol levels dropped when participants were on the LFD W regimen compared to all the other regimens.

Previous trials of walnut supplementation have also demonstrated significant benefits on cholesterol levels.^{7 8 9 10} As those trials were always accompanied by simultaneous decreases in dietary fat from other sources, however, researchers could not conclusively determine whether the walnuts or the dietary fat restriction was responsible for the improvements in cholesterol. The new study found that the LFD alone was not sufficient to lower cholesterol, but that cholesterol levels did drop when walnuts were added to the low-fat diet (LFD W).

Aren’t walnuts high in fat?

How could eating high-fat walnuts lead to lower cholesterol and no weight gain? The addition of walnuts in the HD W and LFD W segments of the study added nearly 400 calories per day to the participants’ diets. In fact, participants in the LFD W group ate more calories from fat (33.7%) than did those participants eating the HD (31.4%). Still, they didn’t gain weight. Participants on the LFD experienced significant weight loss (about 3 pounds) compared to those in the HD group. But even after walnuts were added to their diet, they didn’t put the weight back on. The reasons why are not entirely clear and require further investigation.

Despite the favorable changes to cholesterol levels observed in this study, there are also potential concerns about dramatically increasing the intake of nuts. Although not observed in this study, weight gain is possible since nuts are high in fat. More seriously, nuts are high in alpha-linolenic acid (ALA), which has been linked to an increased risk of cancer, particularly of the prostate.^{11 12 13 14} It is not known why ALA, an omega-3 fatty acid that is generally considered to be health promoting,^{15 16} is associated with increased prostate cancer risk. Other omega-3 fatty acids, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) found primarily in fish oil, appear to reduce the risk of prostate cancer.¹⁷ Men at risk for prostate cancer may wish to choose nuts other than walnuts that are higher in monounsaturated, rather than polyunsaturated, fats. These include almonds, hazelnuts and macadamia nuts, all of which, like walnuts, have been shown to exert beneficial effects on cholesterol levels.^{18 19 20}