More Polyunsaturated Fat to Shrink Waistlines
By Mark Messina, PhD, Executive Director, Soy Nutrition Institute
While body mass index (BMI) is a useful metric for assessing obesity within populations, it falls short for individual assessment. Specifically, it doesn’t distinguish between lean and fat tissue. Nor does it provide information about body fat distribution. Abdominal obesity, also known as central obesity, is the most important factor in determining health risk. Although often not appreciated, intriguing evidence suggests that polyunsaturated fat can help to reduce central obesity.
There is a strong correlation between central obesity and cardiovascular disease,1 diabetes,2,3 and Alzheimer's disease as well as other metabolic and vascular diseases.4 A simple non-invasive measure of central obesity is waist circumference or the waist to hip ratio.5
But the subcutaneous fat found just beneath the skin isn’t the culprit. It’s the fat inside the abdomen, called visceral fat that raises risk. Visceral fat, also known as organ fat or intra-abdominal fat, is located inside the peritoneal cavity, packed in between internal organs and torso. Visceral fat appears to be harmful because, at least according to one theory, it releases metabolic products directly into the portal circulation, which carries blood straight to the liver. As a result, visceral fat cells that are enlarged and stuffed with excess triglycerides pour free fatty acids into the liver. Free fatty acids also accumulate in the pancreas, heart, and other organs. The result is organ dysfunction, which produces impaired regulation of insulin, blood sugar, and cholesterol, as well as abnormal heart function.
From a public health standpoint, reducing abdominal obesity is the most important goal of weight management approaches. New evidence suggests that polyunsaturated fats (PUFA) could help. Swedish researchers conducted a cross-sectional study that included nearly 4,000 60-year old men and women. They assessed serum cholesteryl ester fatty acid composition by gas chromatography and compared it to abdominal obesity prevalence and other anthropometric measures.
The results showed that higher levels of serum palmitic acid (the primary dietary fatty acid) was positively associated with abdominal obesity (multivariate adjusted odds ratio, 1.46; 95% confidence interval: 1.20, 1.77). In contrast, serum linoleic acid was inversely related to abdominal obesity (OR, 0.40; 95% CI: 0.32, 0.49). Serum alpha-linolenic acid level was also inversely related to abdominal obesity.6
Epidemiologic studies aren’t designed to establish cause and effect relationships. And certainly, the results of a cross-sectional study aren’t a sufficient basis for making definitive conclusions. But this newly published Swedish research is consistent with previously published observational7,8 and clinical9,10 data, which link PUFAs to lower rates of abdominal obesity.
These new findings are one more reason why replacing saturated fat with PUFA is a wise approach to lowering risk for chronic disease. Soybean oil and full-fat soyfoods are excellent sources of both linoleic acid and alpha-linolenic acid.