Study under review: Effects of Dietary Protein and Fat Content on Intrahepatocellular and Intramyocellular Lipids during a 6-Day Hypercaloric, High Sucrose Diet: A Randomized Controlled Trial in Normal Weight Healthy Subjects
Ectopic fat storage occurs when fats are stored in places other than subcutaneous adipose tissue, which is where most fat is stored under healthy conditions, or in the visceral fat. In fact, the Greek roots for the word “ectopic” literally mean “out of place.” Common ectopic sites include the liver, pancreas, skeletal muscle, and the heart. The root cause of ectopic fat deposition is unknown, but, as laid out in Figure 1, it is thought to occur when adipose tissue has an impaired ability to store additional fat through decreased expandability. When triglycerides are redirected and stored in organs such as the liver or skeletal muscle, where very little fat is typically stored, it can lead to an impairment of normal organ function and is associated with disorders such as insulin resistance and type 2 diabetes.
A systematic review concluded that a hypercaloric diet with excessive sugars can increase ectopic fat deposits, particularly in the liver and skeletal muscle. Because of this, several overfeeding studies have been conducted in order to examine how excessive nutrition impacts ectopic fat storage, insulin resistance, and other aspects of metabolism such as energy expenditure. One such study compared the effects of overfeeding with either glucose or fructose in healthy men. The hypercaloric diet the participants were given amounted to about 35% additional calories on top of a weight maintenance diet. The researchers found that both sugars increased liver fat storage and fasting triglyceride levels, while only overfeeding with glucose led to increase fat storage in skeletal muscle tissue.
There is also a suggestion that a high protein intake might mitigate the increases in liver fat or muscle fat deposition caused by overfeeding. In one study, participants were fed either a hypercaloric high fat or high fat and high protein diet for four days. The diet containing the high protein levels was able to significantly reduce the increase in liver fat, compared to the lower protein, high fat diet.
However, ectopic fat storage comparisons of sucrose overfeeding with diets consisting of different fat and protein concentrations have not been performed in humans. The closest study so far has been a sucrose overfeeding study in rats given diets of varying fat and protein concentrations, which also resulted in a blunting effect of protein with respect to increased fat deposition. The study under review is the first such study to compare sucrose overfeeding between diets differing in fat and protein levels, and how that impacts ectopic fat storage in humans.
Ectopic fat deposition, which can be promoted by hypercaloric diets, has been linked to organ malfunction and corresponding disorders such as insulin resistance and diabetes. Overfeeding studies have shown that protein may help reduce the levels of ectopic fat deposition. However, overfeeding studies using sucrose while also varying the protein content of the experimental diets have only been performed in rodents. The study under review is the first to examine the macronutrient interactions in humans.
Other Articles in Issue #53 (March 2019)
Does calcium reduce the risk of pre-eclampsia?
Pre-eclampsia is a blood pressure-related problem seen in some pregnant women. Calcium has been found to correlate with its risk, but whether calcium supplementation in early pregnancy can help prevent pre-eclampsia is unclear.
Interview: Abby Langer, BSs, RD
We chat with nutritionist Abby Langer about her journey as a nutritionist, her reviews of diet plans, and what she hopes to take on in 2019.
How much does the cholesterol people eat in their diet actually impact their blood lipids?
Beer before wine or wine before beer? Either way, you’ll be hungover.
Some common drinking folk wisdom is put to the test.
Mini: How does exercise compare to medication for lowering blood pressure?
Exercise is a major lifestyle change that can lead to lower blood pressure. How much lower depends on how high the blood pressure is to start with.
Will eating breakfast keep you lean?
A lot of the evidence supporting the idea that eating breakfast is important for shedding pounds comes from observational studies. Do clinical trials support this claim, too?
Better mood with healthy food?
How much does diet impact depression and anxiety? This meta-analysis aimed to find out.