Results of a small study suggest that returning to a diet high in starch and refined grains after weight loss with a very low-carbohydrate diet may increase body inflammation by activating immune cells and inflammatory pathways; a finding that emphasizes the importance of the type of carbohydrate consumed, not just its amount.
Low-carbohydrate diets are one of the most popular methods for weight loss. Even 2024 data show 7 percent of Americans followed such a diet. Studies have also shown that low-carbohydrate diets can have significant benefits. However, we know maintaining low-carbohydrate diets long-term is difficult and many people may want to return to less restrictive eating patterns after reaching their desired weight. But what happens in your body when you stop the low-carbohydrate diet and start eating carbohydrate-rich foods again?
ScienceDaily writes that scientists examined this question in a new study published in Cell Press Blue. The results indicate that returning to a high-carbohydrate diet may have different health consequences, but apparently these consequences depend on the type of carbohydrate consumed.
Researchers analyzed data from a controlled feeding trial. The initial cohort of this trial consisted of 54 women and men aged 18 to 50, all of whom were overweight or obese at baseline but without cardiovascular disease or diabetes. In the run-in phase, all participants were placed on a very low-carbohydrate diet and were provided with prepared meals designed to produce a substantial 40 percent calorie deficit to induce weight loss.
After participants lost about 15 percent of their weight, they were randomly assigned to three dietary groups and followed different diets for 10 weeks. During this 10-week period, one group continued the very low-carbohydrate diet and the other two groups were assigned two different types of high-carbohydrate diets.
The macronutrient composition in both high-carbohydrate diets was the same: 57 percent carbohydrate, 25 percent fat, and 18 percent protein. However, in one of these diets, 20 percent of total energy was supplied by starch from refined grains, and in the other diet, the same proportion of energy came from added sugar.
The results showed that this single difference apparently created a notable divergence between the two high-carbohydrate groups, and not all carbohydrates are the same in terms of their effect on inflammation.
Blood tests of about 40 participants showed that the high-starch diet, compared with the other two diets, produced signs of increased inflammation and activated a range of immune cells and inflammatory pathways. Among these changes were increased levels of circulating "adipsin" - a signaling protein associated with inflammation - and increased markers of immune cell activation, including +CD4 T cells and neutrophils.
Complementary evidence from a mouse experiment also showed increased immune activity in animals fed maltodextrin, a starch-derived substance, after a period of fasting. This result likewise suggests that starch can affect the immune system.
Activation of the immune system is not necessarily harmful, but it may indicate chronic inflammation; a condition associated with obesity that can play a role in the development of cardiovascular disease and cancer.
Unlike the high-starch group, the high-sugar group showed the lowest level of immune activation compared with all three groups. However, the researchers emphasize that this result does not mean a high-sugar diet is beneficial, and the reduced activity of inflammatory pathways in the carbohydrate diet containing sugar should not be interpreted as an overall benefit of consuming sucrose or fructose, because suppression of complement-dependent immune responses could weaken the body's defensive capacity.
Researchers proposed possible explanations for the higher inflammation in the high-starch group. Refined grains have been associated with markers of low-grade chronic inflammation. One known mechanism for this association is their ability to raise blood glucose after meals, as measured by glycemic index. A sudden rise in glucose may activate the complement system of the immune system; a process that can lead to activation of other inflammatory pathways.
It should be noted that this study was small, and future research with larger groups can provide more information about the effects of carbohydrate-rich diets. The researchers also acknowledged that the 10-week trial period may not accurately reflect the chronic consequences of these diets in real life due to possible physiological adaptation of the body over time.
Nevertheless, the main finding of this study in current conditions indicates that we should pay attention not only to the amount of carbohydrate in the diet but also to its type, and that high-starch diets can become a factor increasing inflammation after weight loss with very low-carbohydrate diets.