Two sides of the same fat family: one fuels type 2 diabetes while the other fights it
A new study has found that two variants within the same fatty acid family have opposite effects on type 2 diabetes risk. The findings, reported by Science Daily on Saturday, introduce a probing nuance to how broad the definition of "saturated fat" in dietary recommendations actually is.
The study focused on the difference between two fatty acid variants: palmitic acid (C16:0) and heptadecanoic acid (C17:0). Both belong to the saturated fatty acid class and are found in foods such as dairy products and red meat. Lead author Dr Anastasia Karagiannis told Science Daily that "treating all saturated fats as a single category is no longer a sustainable position in nutrition science."
In the study, about 12,500 adults in the United States and the United Kingdom were followed for seven years. Participants' serum levels of palmitic and heptadecanoic acid, their diets, and their health status were measured regularly. The results showed that high palmitic acid levels increased the risk of type 2 diabetes by 23 percent, while high heptadecanoic acid levels reduced the risk by 28 percent.
This opposing effect is explained by the different functions of the two fatty acids in metabolic pathways. Palmitic acid disrupts the function of insulin receptors in liver and muscle cells and so contributes to insulin resistance. Heptadecanoic acid, by contrast, has been shown in animal model studies to improve glucose tolerance test performance.
Heptadecanoic acid is an odd-chain fatty acid naturally found in red meat, full-fat dairy products and fermented dairy products (yogurt, some cheeses). The study noted that this fatty acid is relatively low in the modern Western diet because of the reduced consumption of full-fat dairy products over recent decades.
The clinical implications of the study are contested. Some nutrition experts suggest that the results could justify increasing consumption of full-fat dairy products. Others say that the risk of cardiovascular disease must also be taken into account, and that raising consumption of full-fat dairy products could carry other potential health consequences.
Dr Jennifer Williams of the American Diabetes Association told Science Daily that "this is growing evidence that dietary recommendations need to move beyond a traditional approach." Williams said that the conventional advice to "cut saturated fat" should be re-examined in a more nuanced manner.
Another finding of the study is that heptadecanoic acid levels may also be produced by the gut microbiota rather than solely from dietary intake. Gut bacteria, while metabolizing other fats, can release small amounts of heptadecanoic acid as a by-product. This could be a potential target for future probiotic interventions.
Limitations of the study include the lack of supplementary feeding under controlled conditions. The researchers said a randomized controlled trial testing the observational associations is needed. In addition, because the study population was largely of European origin, the general effect should be confirmed in other ethnic groups.
The results were published in the journal Nature Metabolism. The US National Institutes of Health (NIH) and the United Kingdom's Wellcome Trust were among the funders of the study. NIH Nutrition Director Dr Andrew Bremer described the findings as "a structural step toward a more nuanced future for nutrition science."
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