What Are The Benefits?
The benefits of a diet comprised mostly of polyunsaturated fats are well documented. The essential fatty acids omega-3, 6, and 9 must be obtained from food sources. These fatty acids are the precursors for several classes of hormones and comprise most of our cell membranes. Studies are now suggesting that the omega-3 fatty acids are our friends in a number of ways. Since our modern diet typically is high in omega-6 fatty acids and low in omega-3 acids, it may prudent to increase our consumption of foods that contain a higher amount of omega-3 fatty acids. The richest source of omega-3 fatty acids is fish oil from cold water fish.
Omega-3 fatty acids improve insulin action and glucose metabolism in fat and muscle cells. The fatty acids in the phospholipid layer of cell membranes determine the physiochemical properties of the membranes. This in turn influences the cellular functions, especially hormone responsiveness. Increasing the membrane content of polyunsaturated fatty acids increases membrane fluidity and the binding of many hormones to their respective receptors, thereby increasing their action.
They also decrease plasma triglyceride levels. This is hypothesized and supported by studies to play a role in increasing insulin action. It involves fuel switching due to increased utilization of glucose. It is also thought that fish oil supplementation reduces insulin secretion.
Another important aspect is that a diet derived mostly of it fatty acids from fish oils (high 0-3:0-6/9) was shown to reduce white adipose tissue mass, or body-fat, significantly. This has been demonstrated repeatedly in rat models, and also in humans. While omega-3's also increased thermogenesis in brown adipose tissue in rats, that probably has less significance for humans. However, they have detected much lower levels of enzyme activity for fatty acid synthesis in fish oil fed rats (and in vitro human fat cells) than in those fed diets with omega-6, omega-9 and saturated fats. Rats fed diets with omega-3 lost more fat mass (and had much lower triglyceride levels) than those fed a low-fat, high carb diet that was matched for calories.
They have shown in both rats and humans that the composition of adipose fatty acids basically resembles the fatty acid composition of the diet. However, those eating diets high in fish oil EPA and DHA (omega-3's) were not stored in the adipose tissue in similar proportion to the concentrations in the diet. Therefore, these fatty acids may be preferentially oxidized and not stored. Thus, such rapid fatty acid oxidation might prevent a significant portion of lipid accumulation.
The other positive benefit is the consumption of a diet high in 0-3 induced an increase in UCP2 in white adipose tissue. Increased UCP2 uncoupling is associated with reductions in body weight and white adipose tissue.
Interestingly, a reduction of leptin levels, the fat-stat hormone, was reported with high omega-3 consumption. However, as most of the researchers stated in these studies, this may be an artifact simply due to the reduction in fat mass (leptin is secreted by fat cells).
However, in the studies that reported this, they also demonstrated a sustained decrease in appetite and no change in energy expenditure concomitant with decreased leptin levels, which indicates that decreased leptin levels may not be a concern unless they become acutely low, such as in a lean person. In that case, rotation or a blend of fatty acid sources would be necessary. But considering that our diet typically contains a high ratio of o-6:o-3, that may still be a moot point.