High versus low fat diets for insulin sensitivity

Insulin is a hormone that regulates several physiological functions, such as promoting glucose uptake from the blood, inhibiting glucose release by the liver, and inhibiting fatty acid release from fat tissue. Insulin’s role is so central to our survival that nearly every cell in the body contains insulin receptors. When these cells become less sensitive to insulin’s signal, more insulin must be secreted by the body to compensate. This combination of insulin resistance and compensatory hyperinsulinemia may be a fundamental driver^[1] of metabolic syndrome and non-alcoholic fatty liver disease.

As depicted in Figure 1, typical insulin resistance is thought to be caused in part by excessive inflammation^[2] brought about by an abundance and dysfunction^[3] of fat cells. The last few decades has seen an accumulation of evidence showing that fat surrounding organs (visceral or intra-abdominal) is particularly detrimental^[4] in this regard. However, the traditional view that fat beneath the skin (subcutaneous) is less detrimental or even protective when compared to visceral fat has been challenged^[5] recently. In either case, the commonality is that there is an excess amount of fat tissue.

Weight loss has been shown to reduce inflammation^[6] and increase insulin sensitivity^[7]. Moreover, improvements in insulin sensitivity have been shown to correlate most strongly with the magnitude of change in visceral fat. Indeed, fat loss appears to be the primary determinant^[8] of improvements in insulin sensitivity regardless of whether the individual is consuming a low-fat or low-carbohydrate diet. However, not everyone who is over-fat and insulin resistant is actively seeking to lose weight.

The study under review sought to examine the effects of diets differing in their total and saturated fat content on measures of insulin sensitivity and glucose tolerance during weight-stable conditions. Researchers also investigated whether these changes were mediated through changes in body fat distribution.

Figure 1: How inflammation may contribute to the development of diabetes

Insulin resistance is considered a hallmark of metabolic syndrome and fatty liver. It is commonly brought about by fat cell-mediated inflammation. Although fat loss has been shown to improve insulin sensitivity and inflammation regardless of dietary composition, not everyone who is insulin resistant and inflamed is seeking to lose weight. Thus, the current study sought to compare the effects of a high-fat diet to a low-fat diet on insulin sensitivity during weight-stable conditions.