Having a hard time losing weight? It just might be your metabolism after all, new research from Touro College suggests.
People who lost nearly 100 pounds through weight loss surgery showed no change in how efficiently they burned calories, Joseph Indelicato, PhD, the Chair of the Touro College Research Collaborative at Touro College School of Health Sciences in Bay Shore, New York, found. “They lost an average of 99 pounds, and their metabolism didn’t speed up at all,” he explained.
What this means, he added, is that even after weight loss surgery, a formerly obese person would need to eat far fewer calories than a normal-weight person in order to maintain their weight loss.
To measure people’s calorie-burning efficiency, Dr. Indelicato took resting metabolic rate (RMR) – the amount of calories a person needs to burn at rest per day in order to maintain their body weight – and divided it by weight. The result is the metabolic factor (MF), which shows how many calories a person burns per pound of their body weight. The higher the MF, the faster the metabolism.
In a previous study, Dr. Indelicato and his colleagues found that obese people had an average MF of 8.3 calories per pound, compared to 10.6 for overweight people and 12.8 for normal-weight individuals This means that an obese person needs just eight calories per pound to maintain his or her body weight, while a normal-weight person burns 12 calories per pound while at rest – 50% more.
In the new study, published online in Obesity Surgery, Dr. Indelicato looked at 18 bariatric surgery patients. While patients’ average RMR went from 2,634 calories before the surgery to 1,954 calories afterwards, their MF barely budged, going from 8.1 calories per pound before surgery to 8.6 pounds afterwards, not a statistically significant difference. “The metabolism was slow to begin with, it stayed slow a year after surgery,” he said. “These people just have slow metabolism.”
So a person who is obese and wants to lose weight will need to eat far fewer calories, and keep eating that way to maintain a normal weight, according to Dr. Indelicato. “Would you make an active decision to spend the rest of your life on 1,200 calories a day?” he asked. “If you’re going to go on a diet, if you’re serious about losing weight, this is the end game, and it’s a different conversation.”
The RMR test is readily available, and learning your MF – RMR divided by your weight in pounds – can be very useful, Dr. Indelicato said. The testing technique, which is called indirect calorimetry, involves breathing into a tube for 10 minutes to measure the volume of oxygen inhaled and the volume of carbon dioxide exhaled. The RMR test is billable under most insurances, according to Dr. Indelicato.
“The take-away may be that before someone starts dieting or going for surgery, it would be useful to know that number in order to figure out what diet level that they would need,” he said.
The researcher said he hopes his findings will help reduce the stigma that obese people face, because they show that a person’s MF – not their willpower – plays the biggest role in determining their weight status.
The next steps in the research, according to Dr. Indelicato, will be to find out when a person’s MF is set. “Are we talking about something triggered by diet or heredity? Those studies need to be done,” he said. The current findings also need to be replicated by other researchers, he added.
The Touro Research Collaborative is a dedicated group of faculty who pursue research in the medical and health sciences.