A NEW study revealed that restricting carbohydrates, even without cutting overall calories, can produce metabolic effects similar to fasting, offering fresh insights into how diet composition impacts post-meal metabolism and potential strategies for cardiometabolic health.
In a carefully controlled crossover trial, researchers from the University of Surrey led by Hayriye Biyikoglu, Dr. M. Denise Robertson, and Dr. Adam L. Collins evaluated the acute metabolic responses of 12 healthy overweight or obese participants to three different diets. Each participant consumed: a standard carbohydrate, energy-balanced diet (55% carbs), a low-carbohydrate, energy-balanced diet (50 g/day carbs), and a low-carbohydrate, energy-restricted diet (50 g/day carbs with a 75% calorie cut), each for 36 hours with washout periods in between.
Both low-carb diets, regardless of calorie intake, led to notable reductions in blood triglycerides and respiratory quotient, along with elevated levels of fatty acids and ketones (3-hydroxybutyrate), markers consistent with increased fat oxidation and metabolic shift toward ketogenesis.
Interestingly, post-meal glucose levels rose in the low-carb energy-balanced group, a likely consequence of lowered insulin secretion not mirrored by corresponding insulin spikes. Appetite and energy expenditure were not significantly impacted by either energy or carbohydrate restriction.
“These results suggest that short-term carbohydrate restriction can trigger many of the same metabolic pathways as fasting,” said Dr. Collins. “What’s most compelling is that these effects can occur without reducing calorie intake, meaning carb cycling may offer a new route to metabolic health without the need for prolonged fasting or severe energy restriction.”
The researchers propose that regular, brief cycles of carbohydrate restriction could become a promising and more sustainable dietary strategy for improving cardiometabolic health. Further research is now needed to assess long-term benefits and applicability in larger, more diverse populations.
Aleksandra Zurowska, EMJ
Reference
Biyikoglu et al. Isolating the acute metabolic effects of carbohydrate restriction on postprandial metabolism with or without energy restriction: a crossover study. Eur J Nutr. 2025;DOI: 10.1007/s00394-025-03646-5
