NEW YORK, May 11: Intermittent fasting has proven to be an effective tool for weight loss and offers significant benefits for metabolic health, even independent of weight loss. However, some individuals find the more extreme forms of intermittent fasting, such as the 5:2 diet, challenging due to the severe calorie restriction required on fasting days.

New research suggests that you don't need to drastically cut calories to experience the metabolic benefits of intermittent fasting. In fact, restricting carbohydrate intake twice a week may be enough to see improvements in metabolic health.

Intermittent fasting enhances health by impacting metabolism in key ways. After eating, the body enters the postprandial state, where it uses carbohydrates for immediate energy while storing some for later use. However, during periods of fasting, the body shifts to burning fat for energy, enhancing metabolic flexibility. This balance between carbohydrate and fat usage leads to better cardiometabolic health, reducing the risk of conditions like cardiovascular disease, insulin resistance, and type 2 diabetes.

Previous studies by my team have shown how fasting influences fat burning. For example, following a day of fasting or severe calorie restriction (around 25% of daily calorie requirements), participants were able to more effectively burn fat after consuming a high-fat meal, such as a full English breakfast. This shift from using carbs to burning fat was observed both during the fast and the following day.

In other research, we compared intermittent fasting with a calorie-restricted diet where participants lost 5% of their body weight. Despite the same weight loss results, the intermittent fasting group exhibited better improvements in metabolic health. This was a consistent finding in several studies on intermittent fasting and its positive effects on metabolism.

However, why exactly is intermittent fasting beneficial for metabolic health? This is a question I explored in my latest study. On typical fasting days, especially for those following the 5:2 method, calorie intake is very low, resulting in a drastic reduction in carbohydrate consumption. Since the postprandial state is governed by carbohydrate availability, it raised the question: Is it the calorie restriction, or is it the carbohydrate restriction that drives the metabolic changes seen with intermittent fasting?

To answer this, we recruited 12 overweight and obese participants. They were given a very low-carb diet on one day and a severely calorie-restricted diet (about 75% fewer calories than usual) on another day. After each fasting day, they were given a high-fat, high-sugar meal, like an English breakfast, to observe how their bodies burned fat.

Our results showed that both the low-carb day and the calorie-restricted fasting day resulted in similar improvements in fat burning and fat handling. This suggests that restricting carbs could trigger the same favorable metabolic effects as fasting.

While our findings are promising, further studies with a larger sample size are needed to confirm these results. If this approach proves effective, it could help address some of the practical challenges people face with intermittent fasting and low-carb diets.

For example, severe calorie restriction during fasting days can lead to nutritional deficiencies and trigger disordered eating behaviors. Similarly, long-term carb restriction can be hard to stick to and may create an unhealthy fear of carbohydrates. Moreover, both intermittent fasting and continuous carb restriction are likely to result in weight loss, which may not be desirable for those looking to improve health without losing weight or for those aiming to maintain their weight.

We are now exploring the potential of a modified intermittent fasting approach: intermittent carb restriction. Instead of severely restricting calories, participants would limit carb intake two days a week. If this approach proves effective, it would allow people to benefit from fasting's metabolic advantages without the need to cut calories on fasting days.