11 Std. ·
New study compares high-fat to high-carb overfeeding and reports that overeating fat is more detrimental to insulin sensitivity (https://www.ncbi.nlm.nih.gov/pubmed/28768703).
This study involved nine lean, healthy men who were regularly active and in decent shape (VO2max of 52 mL/kg/min). Participants ate an experimental diet for three days that provided 75% more energy than required to maintain weight, supplied as high-fat (12% pro; 78% fat; 10% cho) or high-carb (11% pro; 9% fat; 80% cho). These diets were compared to a weight-maintenance control diet (14% pro; 24% fat; 62% cho). In other words, subjects ate about 496 grams of fat and 1137 grams carbohydrate during the high-fat and high-carb diets, respectively.
Importantly, the high-fat diet was high in unsaturated fats (34% mono; 34% poly; 10% sat) and the omega-6/-3 ratio and fiber intake was similar between conditions. It also utilized mostly whole-foods. For instance, the high-fat breakfast was avocado and walnuts while the high-carb breakfast was wheat bread with skimmed milk and fig spread.
Using the gold-standard hyperinsulinemic-euglycemic clamp, whole-body insulin sensitivity was significantly reduced by 17% after overeating fat compared to the control, whereas it was significantly increased(!!!) by 26% after overeating on carbohydrates. Glucose uptake into skeletal muscle was 20% lower with high-fat and 41% higher with high-carb. Also, resting energy expenditure was significantly reduced with high-fat and increased with high-carb.
Notably, these effects were observed alongside no changes in insulin signaling in either group. This is interesting considering that high-fat feeding resulted in significant increases in diacylglycerol content of skeletal muscle (by 37%) and increases in intramuscular triglycerides (by 52%), both of which could interfere with insulin receptor function. It is possible that negative effects of this buildup of fat take longer than 3 days to be apparent. The study at hand thus suggests an alternative mechanism causes insulin resistance in the short-term.
It isn’t all fun in games for high-carb though, at least not in the liver. The high-fat diet actually improved hepatic glucoregulation and lowered de novo lipogenesis, while high carbohydrate intake induced hepatic insulin resistance and an increase in plasma triglyceride levels that approached hypertriglyceridemia.
The bottom line? Don’t overeat by 75% of your daily energy requirements for 3 days!