Diet Transitions and Metabolic Responses
Many people turn to low-carbohydrate diets to shed excess weight. Data from 2024 shows roughly 7 percent of Americans follow these plans. Recent studies indicate that strict low-carb protocols can improve metabolic health and liver function during the weight-loss phase. Still, maintaining such restrictive habits over a long period proves difficult for most individuals. When weight goals are met, participants often return to diets containing more carbohydrates.
Researchers from NYU Langone Health conducted a controlled feeding experiment to see what happens when the body transitions back to a high-carb intake. Their work, published in Cell Press Blue, tracked 54 participants aged 18 to 50. Everyone in the group started out as overweight or obese but did not have existing cardiovascular disease or diabetes. The researchers used a two-phase model to isolate the physiological effects of specific carbohydrate types.
Experimental Design and Participant Data
All participants began with a run-in phase involving a very-low-carbohydrate diet. This period featured prepared meals designed to trigger a 40 percent calorie deficit. Once individuals reached approximately 15 percent weight loss, the team split them into three groups for a 10-week follow-up. One group remained on a very-low-carb diet while the others consumed high-carb alternatives.
Both high-carb groups consumed identical macronutrient ratios of 57 percent carbohydrate, 25 percent fat, and 18 percent protein. The crucial distinction lay in the source of the carbohydrates. One group received 20 percent of their energy from refined grain starch. The other group consumed an equal proportion of added sugar. This specific difference caused measurable changes in the participants' biological markers.
Inflammation and Immune System Activation
Blood analysis from 40 of the participants showed a sharp divide between the diets. The high-starch group displayed clear signs of increased inflammation compared to the low-carb and sugar-heavy groups. This response activated several immune cells and inflammatory pathways. Researchers noted higher levels of adipsin, a signaling protein often associated with inflammation. They also recorded increased activation of CD4+ T cells and neutrophils.
Experiments with mice provided further context for these findings. Animals fed maltodextrin after fasting showed similar immune activity. The study authors suggest that starch acts as an unrecognized driver of inflammation following a period of weight loss on low-carb diets. High glycemic index foods cause rapid blood glucose spikes, which may trigger the body’s complement system.
Interpreting the Findings
While the sugar-heavy group showed lower levels of immune activation, the authors caution against viewing this as a health benefit. They state that suppressing immune responses can impair basic host defense mechanisms. Furthermore, this study lasted only 10 weeks and involved a small sample size. Larger trials are necessary to confirm how these diets affect the body over many years.
Physiological adaptation might change these outcomes in real-world settings. Still, the data underscores that not all carbohydrates impact the body in the same way. The type of carb matters. People who lose weight on low-carb diets should watch the composition of their meals as they reintroduce carbohydrates.