Does eating less slow your metabolism? Nutritionists explain what happens when you diet

Many people trying to lose weight worry that eating less could slow down their metabolism, making it harder to burn calories and keep the weight off.

According to nutrition experts, while the body naturally adapts to prolonged calorie restriction, metabolism does not permanently slow down from dieting alone.

Instead, the biggest concern is losing muscle mass, which plays a key role in how many calories the body burns at rest.

Bernice Sabenicio, a nutritionist-dietitian at Reshape Slimming & Fitness Club, said metabolism can decrease during long periods of calorie restriction as the body tries to conserve energy.

"Yes, dieting can slow metabolism, but this is usually temporary, especially when calories are reduced for a long period of time. So ito 'yung natural way ng katawan natin to save energy, and this is called metabolic adaptation," Sabenicio said.

She explained that several factors contribute to this process.

"Kapag masyadong konti ang kinakain natin, our body reduces energy use to conserve fuel. Dahil nga nagdidiet ka, hindi lang fat ang nawawala, pati muscle din. Since muscle helps burn calories, the less muscle you have, the lower your resting metabolism can be," she said.

Resting metabolism refers to the minimum number of calories the body burns while at rest to perform essential functions such as breathing, keeping organs functioning, and pumping blood throughout the body.

Meanwhile, Christian Jay Vasquez, a public health nutritionist-dietitian with the Pasig City Nutrition Committee, echoed that muscle loss — not simply eating less — is what can reduce resting metabolic rate over time.

"If an aggressive dieting strategy causes an individual to lose substantial muscle tissue due to protein malabsorption, their resting metabolic rate (RMR) will drop. In the long run, this makes weight maintenance considerably harder, proving that the composition of the weight lost matters just as much as the number on the scale," Vasquez said.

Vasquez added that extreme fasting may also make it difficult to consume enough protein throughout the day to maintain muscle.

"Sports nutrition research emphasizes that maximizing muscle mass requires spacing out protein boluses across three to four distinct feeding windows to repeatedly trigger muscle protein synthesis," he said.

Still, Vasquez said that calorie deficit and intermittent fasting can benefit long-term metabolic health when practiced properly, citing benefits such as improved insulin sensitivity, lower blood pressure, and reduced inflammation.

Sabenicio emphasized that dieting should not focus solely on eating less, but on ensuring the body continues to receive adequate nutrition.

"These are just some of the factors that can affect metabolism while dieting. Kaya if you're on a diet, make sure to have an assessment with a dietitian para malaman kung hanggang saan lang ang safe limit ng pagbaba ng calorie intake ng katawan mo. And of course, physical activity is important to help retain muscle, especially resistance training," she said.

"There is no one-size-fits-all diet because we all have different bodies, lifestyles, and nutritional needs."

She encouraged Filipinos to follow Pinggang Pinoy, developed by the Food and Nutrition Research Institute (FNRI-DOST), and practice moderation, variety, and balance in their meals.

"Healthy eating is about nourishing your body — not restricting it. Be kind to yourself and focus on consistency over perfection," she said. —JCB, GMA News