Low-carbohydrate diets are one of the most popular options for losing weight, with data suggesting 7 percent of Americans followed a low-carb diet in 2024.
Research also shows that low-carbohydrate diets can have significant benefits, with one recent study finding a strict low-carb keto diet outperformed other weight-loss options for several markers of metabolic health and liver function.
But we know that low-carb diets are difficult to maintain in the long term, and many people might want to return to less-restrictive eating patterns if they achieve weight or other health goals.
So what happens to your body when you come off a low-carb diet, and resume eating foods that are high in carbohydrates?
In a new study in Cell Press Blue, scientists explored that question, and the results suggest that returning to a high-carb diet may have a range of consequences for health, but it seems to depend on what kinds of carbohydrates you eat.
A team led by researchers from NYU Langone Health analyzed data from a controlled feeding experiment, involving an initial group of 54 participants made up of both men and women aged 18–50 years.
At the outset, all the participants were overweight or obese, but didn't have cardiovascular disease or diabetes.
During a run-in phase, all the participants received a very-low-carbohydrate diet, made up of delivered prepared meals designed to produce a substantial 40 percent calorie deficit that would produce weight loss.
After participants achieved ~15 percent weight loss, they were randomly assigned to one of three different dietary groups for 10 weeks.
During this 10-week phase, one group continued on very-low-carbohydrate diets, while the two other groups received different kinds of high-carbohydrate diets.
Both the high-carb diets had the same macronutrient composition as each other (57% carbohydrate, 25% fat, 18% protein), but one of the high-carb diets delivered 20 percent of its total energy from starch in refined grains, while the other contained the same proportion from added sugar.
As it turned out, that single alteration appeared to make a considerable difference between the two high-carb groups.
Blood test analyses from approximately 40 of the participants in the experiment showed that the high-starch diet triggered signs of increased inflammation compared to the other two diet groups, activating a range of immune cells and inflammatory pathways.
This included higher levels of circulating adipsin – a signaling protein linked to inflammation – plus increased signs of activation in immune cells including CD4+ T cells and neutrophils.
Additional evidence from an experiment in mice showed that animals fed maltodextrin (derived from starch) after fasting showed increased immune activity, further suggesting that starch can affect the immune system.
While an activated immune system in itself isn't necessarily harmful, it can be an indicator of chronic inflammation, which is associated with obesity, and which can contribute to cardiovascular disease and cancer.
In contrast to the high-starch group, the high-sugar group scored the lowest of all three groups in terms of immune activation, but the researchers are careful to note this doesn't mean a high-sugar diet is good for you.
"Importantly, the reduction in inflammatory pathways in the HC-Sugar group should not be interpreted as an overall benefit of sucrose or fructose consumption, as suppression of complement-mediated immune responses could impair host defense," the researchers write.
As for why the high-starch group saw higher levels of inflammation, the team has some ideas.
"Refined grains have been linked to markers of low-grade, chronic inflammation, with one established mechanism being their ability to increase postprandial [post-meal] blood glucose levels, as quantified by the glycemic index (GI)," the researchers explain.
The researchers say sharp rises in glucose could activate the immune system's complement system, which can trigger further inflammatory pathways.
It's worth noting that this is only a small study, and future research in larger groups of participants could reveal more about the effects of carbohydrate-rich diets.
The researchers also acknowledge that the length of the 10-week experiment may not accurately reflect the chronic effects of these diets in real life, due to the possibility of physiological adaptation over time.
Still, for now, their takeaway finding suggests we ought to be mindful not just about the carbohydrates we eat in our diets, but also what kind of carbohydrates they are.
"Following weight loss with very-low-carbohydrate diets," the team concludes, "starch-rich diets serve as an unrecognized driver of inflammation."
The findings are reported in Cell Press Blue.
This article was fact-checked by Fiona MacDonald and edited by Fiona MacDonald. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.