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A thorough trial of carb intake for diabetes

There are few conditions where carbs play as direct of a role as in type 2 diabetes. Yet the recommended carb intake levels for this condition aren’t so different than for the general population. That may change at some point, due to trials like this one, which is more highly controlled and thorough than previous lower-carb & diabetes studies.

Study under review: Comparison of low- and high-carbohydrate diets for type 2 diabetes management: a randomized trial


Although some diet-related diseases are handled primarily with pharmacological medications, lifestyle interventions are a cornerstone of type 2 diabetes (T2D) management. In the past few issues of Study Deep Dives, we’ve covered recent research on blood sugar management, and Study Deep Dives issue #3 featured an op-ed by Stephan Guyenet on how T2D can be prevented.

But the most widely-debated topic concerning T2D prevention and treatment is probably carbohydrate intake. Traditionally, the American Diabetes Association does not recommend[1] a lower carbohydrate diet for T2D management. However, they also acknowledge that the amount of carbohydrates in the diet is the primary determinant of the blood glucose response to eating.

Because relatively high-carbohydrate diets are often recommended for T2D patients who may be considered carbohydrate-intolerant, there has been growing interest in the use of low-carbohydrate diets that are higher in fat and protein. There is no shortage of research comparing low- and high-carbohydrate diets in various populations, but most use research designs that allow the participants to consume food freely, leading to differences in energy intake and weight change between dietary conditions. No doubt these studies have their advantages by being more applicable to what would occur in real-life, but they give us less information about the mechanisms behind the diets. Additionally, it has been established that caloric restriction and weight loss independently improve glycemic control, insulin resistance, and cardiovascular risk.

Another confounding variable of previous research is the consumption of saturated fat, which usually increases during low-carbohydrate diets, since people tend to replace carb-rich foods with food sources containing high levels of saturated fat, like fattier cuts of meat and dairy. Interestingly, a vegetable-based low-carbohydrate diet has been associated with[2] lower all-cause and cardiovascular disease mortality rates when compared to an animal-based low-carbohydrate diet. Plant-based fats are composed primarily of mono- and polyunsaturated fatty acids, suggesting that the health effects of a low-carbohydrate diet may be influenced by fat type (or food quality!).

The study under review compared the long-term metabolic effects of a hypocaloric low-carbohydrate diet with a high unsaturated to saturated fatty acid ratio to an energy-matched high-carbohydrate diet based on the recommendations of the American Association of Clinical Endocrinologists (AACE) in obese people with T2D, as part of a holistic lifestyle modification program.

Hypocaloric diets for people with type 2 diabetes are known to provide some benefit. However, the ideal macronutrient ratios of such diets aren’t well-understood. Furthermore, studies involving various diets for people with type 2 diabetes are often confounded by an increase in saturated fat intake to compensate for lower carbohydrate intake. The goal of this study was to examine the effects of a calorie-matched hypocaloric low-carb diet with a high unsaturated to saturated fatty acid ratio compared to a high-carb diet in diabetics.

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Other Articles in Issue #10 (August 2015)

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    Although both cheese and meat are lumped into the “watch out!” category in hearthealth recommendations, dairy products often show neutral or positive associations with cardiovascular health. But how do cheese-rich diets fare in randomized trials when compared to other diets? This trial tested three diets against each other in a highly controlled fashion: a cheese diet, meat diet, and high-carb diet.
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    If you run, cycle, or do anything long and sweaty, then you already know that carb intake is especially important for endurance activity. But recommended intakes range from around 30-60 grams, which is pretty broad. This trial can help you get to a more specific number, and possibly perform better.
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    B vitamins are commonly thought of as harmless, due to being water-soluble. As nutrition junkies know, that view lacks nuance, and B vitamins can indeed be harmful in certain situations. As an example, this elegant series of experiments sheds new light on the mechanism by which vitamin B12 may impact acne formation.
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