Calories in vs. calories out? Weight management is not that simple, say researchers

It is a model that is particularly beloved of food and beverage companies – especially those selling high-calorie products – but the idea that weight management is a simple balance between the calories taken in through food and drink and those expended through physical activity increasingly is being called into question.

"This idea is completely false,”​ said Professor John Blundell of Leeds University, who presented a session at the ICN on Tuesday.

"Physical activity is not calorie expenditure converted into weight changes,"​ he said. "Physical activity changes physiology to bring about important health changes, reducing blood pressure, heart rate, and plasma insulin, and increasing cardiovascular fitness which is more important than weight.”​

He said that over 15 years, researchers have compared active and sedentary people of the same age, height and BMI.

“The active people can eat more without going into positive energy balance,”​ he said.

The trials involved supervised exercise programmes, burning 500 calories in five sessions a week at 70% maximum heart rate, and supervising food intake. Over a 12-week period, participants lost an average of 1 kg to 8 kg, although a small group of participants gained weight. However, all participants lost fat and gained fat-free mass.

David Allison of the University of Alabama, Birmingham in the United States also aimed to challenge preconceptions of the calories in vs. calories out equation in a presentation on Tuesday.

“You can’t do just one thing to change energy balance, because as soon as you do, something else happens so you end up doing two or more,”​ he said.

He highlighted some of the ‘myths’ surrounding the idea of energy balance, including the belief that cutting 100 calories a day, or 3,500 calories over 35 days, will lead to weight loss of one pound (about half a kilo). Allison pointed out that as people lose weight, their caloric needs reduce.

Additionally, eating higher calorie meals at restaurants does not necessarily lead to weight gain as people tend to compensate by eating less the day before or after the higher calorie meal, or by exercising more.

“In reality, people compensate for about two thirds of change to energy balance​,” he said, by eating more if activity increases or reducing food intake if activity decreases.