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 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 brought about by an abundance and dysfunction 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 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 recently. In either case, the commonality is that there is an excess amount of fat tissue.
Weight loss has been shown to reduce inflammation and increase insulin sensitivity. 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 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.
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.
Other Articles in Issue #14 (December 2015)
Investigating vitamin D as a performance enhancer
Having sufficient vitamin D levels has been associated with better muscle recovery. This trial not only looks at the question of causality, but also addresses some potential mechanisms of vitamin D’s benefit for exercise.
Trans fats: “natural” might not mean “healthy”
In the nutrition community, a common message has been that artificial trans fats are bad, however natural trans fats are not only okay but beneficial. This trial on blood lipids puts that to the test.
Exercise, with a (tart) cherry on top!
Berries have burst onto the research scene in recent years. Tart cherries have shown some of the most promise in certain areas, leading to this study of powdered tart cherry on exercise recovery.
Interview: Dan Pardi MS PhD(c)
Dan Pardi is an entrepreneur and researcher whose life’s work is centered on how to facilitate health behaviors in others.
Root rage: The impact of ashwagandha on muscle
So called “adaptogens” like ashwagandha are typically studied for stress-easing potential. A randomized trial looked into this popular herb for a different purpose: bolstering adaptations to weight training.
Does the Food Guide make my butt get fat?
By Francy Pillo-Blocka, RD
We’ve covered antioxidants and strength training before. This study is a bit different — it investigates whether vitamin C and vitamin E might impact adaptations to endurance exercise.
I <3 green tea
When it comes to curbing cardiovascular disease, it’s not all about reducing cholesterol. Green tea may help prevent oxidation of LDL, as is explored in this trial looking at green tea catechins both in vivo and in vitro.
Investigating slow carbs for metabolic rate
Glycemic index, glycemic load, insulin index: only one of these is widely known by the public. But when it comes to keeping weight off, does glycemic index and total carb content actually have any impact?