Carbohydrate metabolism: Genetics, Insulin, and Carbs

Sometimes the things that everyone seems to accept as gospel don’t always hold true when researchers actually look into them, especially in regard to nutrition.

Take the glycemic index for example: Since around the 1980s, accepted dogma holds that white bread will very quickly raise everyone’s blood glucose levels with a GI score of 73, while a banana gives a slower increase in glucose with a GI score of 48.

Turns out that when scientists decided to look at a large group of individuals’ glycemic responses to foods, people’s responses vary a lot from what the glycemic index shows.

Individualized Glycemic Response

There have been a couple of good studies over the last couple of years that have shown the huge variation in blood glucose levels in response to carbohydrates. For example, some people may have blood sugar spikes from eating a banana, while others may have their blood sugar drop from eating bread. The individual variation found in the studies is striking.

Researchers summarized the findings on the individual postprandial glycemic responses (PPGR): “we demonstrate on 800 individuals that the PPGR of different people to the same food can greatly vary. The most compelling evidence for this observation is the controlled setting of standardized meals, provided to all participants in replicates. This high interpersonal variability suggests that at least with regard to PPGRs, approaches those grade dietary ingredients as universally “good” or “bad” based on their average PPGR in the population may have limited utility for an individual.”[ref]

Another study looked at the glycemic response of 20 individuals to white bread and to whole wheat sourdough bread. Turns out that for about half the people in the study, white bread caused less of a blood glucose spike, while for the other half, the whole wheat bread was better.[ref]

One reason for the individual variation is the differences in the gut microbes of each individual. The types of microbes in your gut depend on a lot of factors, including early childhood experiences, types of food that you currently eat, antibiotic exposure, and also your genes.

Genetic variations also play a role in how people react to carbohydrates in their diet.

Why is this important? Diet advice is everywhere — from the doctor on TV to your own doctor telling you to drop a few pounds. But generic recommendations may do nothing for you, and if your goal is to prevent type 2 diabetes, the recommendations may actually work against you.

Below are a few genes that affect insulin or glucose levels based on carbohydrate consumption.