New Evidence on Dietary Fat, Blood Sugar, and Insulin Response?

Here we go again. A new study appears to link high fat intake to insulin resistance and postmeal blood sugar spikes. All study participants had Type 1 diabetes and were assigned to consume either two low-fat meals and one high-fat dinner or three low-fat meals. Researchers reported that those receiving the high-fat dinner required more insulin (12.6 units vs. 9 units for the low-fat dinner) and that their postprandial blood sugar and insulin levels were higher and stayed high for several hours after eating.

There are a few red flags regarding this study. First of all, the sample size was extremely small (seven people). And this line is revealing:
 "The two dinners received by each subject had identical carbohydrate and protein content but they differed in fat content (10 grams vs. 60 grams)."

Now, the amount of carbs each meal contained wasn't reported (or at least I couldn't find it), but the amount of calories  was. So by doing some math, we can get a ballpark estimate:

The low-fat dinner contained on average about 600 calories, 10 grams of fat (90 calories), and let's say 25% protein (38 grams, 150 calories), which is probably being generous. That would leave approximately 90 grams (360 calories) of carbohydrate to make the 600 calorie total. 

So given the high carbohydrate content of the meal, these results aren't surprising. Fat delays the absorption of carbohydrate and makes accurate dosing of insulin extremely challenging (as CDE Gary Scheiner explains in discussing how to bolus for pizza).  Previous studies have demonstrated the deleterious metabolic effects of consuming a high-fat, high-carbohydrate meal, which include insulin resistance, delayed postprandial hyperglycemia, and elevated triglycerides. 

However, there is research indicating that a high-fat, low-carbohydrate diet does not produce the same response; in fact, it results in lower insulin needs, less insulin resistance, and better postmeal blood sugar and lipid response  in both Type 1 and Type 2 diabetes. And there's enough anecdotal evidence to support these findings many times over.

So this study simply confirms what we already know: The combination of high fat and high carbohydrate is unhealthy. The best chance people with diabetes have of achieving better blood sugar control and decreasing insulin needs is to adopt whatever form of carbohydrate restriction works best for them.

1. Volek JS, et al. Carbohydrate restriction has a more favorable impact on the metabolic syndrome than a low-fat diet. Lipids 2009 Apr;44(4):297-309.
2.Volek JS, et al. Effects of dietary carbohydrate restriction vs. low-fat diet on flow-mediated dilation. Metabolism
2009 Dec;58(12):1769-77
3. Nielson JV, et al. Low carbohydrate diet int type 1 diabetes, long-term improvement and adherence: a clinical audit. Diabetol Metab Syndr 4: 23, 2012

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