Researchers at the National Institutes of Health have created a mathematical model – and an accompanying online weight simulation tool – of what happens when people of varying weights, diets and exercise habits try to change their weight. The findings challenge the commonly held belief that eating 3,500 fewer calories – or burning them off exercising – will always result in a pound of weight loss.
Instead, the researchers’ computer simulations indicate that this assumption overestimates weight loss because it fails to account for how metabolism changes. The computer simulations show how these metabolic changes can significantly differ among people. Findings will be published Aug. 26 in a Lancet issue devoted to obesity.
However, the computer simulation of metabolism is meant as a research tool and not as a weight-loss guide for the public. The computer program can run simulations for changes in calories or exercise that would never be recommended for healthy weight loss. The researchers hope to use the knowledge gained from developing the model and from clinical trials in people to refine the tool for everyone.
“This research helps us understand why one person may lose weight faster or slower than another, even when they eat the same diet and do the same exercise,” said Kevin Hall, Ph.D., an obesity researcher and physicist at the NIH’s National Institute of Diabetes and Digestive and Kidney Diseases and the paper’s first author. “Our computer simulations can then be used to help design personalized weight management programs to address individual needs and goals.”
The online simulation tool based on the model enables researchers to accurately predict how body weight will change and how long it will likely take to reach weight goals based on a starting weight and estimated physical activity. The tool, at http://bwsimulator.niddk.nih.gov/, simulates how factors such as diet and exercise can alter metabolism over time and thereby lead to changes of weight and body fat.
To test the model, the researchers compared predicted weight changes to actual changes in people. “Mathematical modeling lets us make and test predictions about changes in weight and metabolism over time,” Hall said. “We’re developing research tools to accurately simulate physiological differences between people based on gender, age, height, and weight, as well as body fat and resting metabolic rate.”
For example, the team found that people’s bodies adapt slowly to changes in dietary intake. They also found heavier people can expect greater weight change with the same change in diet, though reaching a stable body weight will take them longer than people with less fat.
The model also points to a potential simplified method to approximate weight loss in an average overweight person. An adult who has a body mass index (a measure of a person’s weight in relation to his or her height) between 25 and 29.9 is considered overweight. One example: For every pound you want to lose, permanently cut 10 calories from your current intake per day. At that rate, it will take about one year to achieve half of the total weight loss, and almost all of the weight loss will have occurred by three years. This calculation shows how long it takes to achieve a weight-loss goal for a single permanent change of diet or exercise. Researchers can use the web simulation tool to plan for a phase of more-rapid weight loss followed by a weight maintenance phase. People should consult with their physician prior to embarking on a diet plan.
“By using our model to track progress, clinicians can help people re-evaluate their goals and ability to achieve them at the pace they want,” Hall said. “It’s a good reality check for how long weight-loss takes, and what changes in eating and exercise are required to achieve and maintain goal weight.”
Moving toward that goal, a more comprehensive mathematical model of human metabolism was used recently to design an NIH clinical trial that is comparing the effects of reducing fats versus carbohydrates in obese adults. Hall and collaborators also published findings in the May 11 issue of the American Journal of Clinical Nutrition illustrating a method for precisely measuring how much a person’s eating changed when he or she went on a diet.
“This research illustrates how the interdisciplinary skills of NIH scientists, like a physicist doing obesity research, can help lead to innovative ways to test, understand and treat a major public health epidemic,” said NIDDK Director Griffin P. Rodgers, M.D. “Advancing research from the laboratory to the bedside enables us to make the discoveries that can better people’s lives.”
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Coauthors on the Lancet paper include Carson Chow, Ph.D., and Dhruva Chandramohan at NIDDK, and researchers at the World Health Organization Collaborating Center for Obesity Prevention at Deakin University in Australia; Columbia University’s Mailman School of Public Health, and Harvard University’s School of Public Health. Additional funding came from the Robert Wood Johnson Foundation, the Centers for Disease Control and Prevention, and the NIH Office of Behavioral and Social Sciences Research.
Advanced Nutrition and Human Metabolism
Medical Biochemistry: Human Metabolism in Health and Disease
Introduction to Nutrition and Metabolism, Fourth Edition
Exercise Metabolism – 2nd Edition
There several important variables that need to be considered. When dieting it is important to have an efficient way to maintain lean body mass. Without this, muscle mass is lost which will reduce metabolic rate. Too much aerobic or other stressful exercise will worsen this situation and result in even greater loss of lean body mass along with increased feelings of hunger. Stress in general is counter-productive to fat-loss due to the release of hormones like cortisol. Food choices that result in elevated insulin levels will halt or sigificantly slow fat-loss so what you eat is actually more important than how much you eat. Dehydration or inadequate hydration will aslo have a negative effect on the rate of fat loss. The general perscription of reduced calories and increased aerobic exercise is a flawed methodology.
This can be a problem. Over weight people have to learn so much in order to change their life around. Adding this is just a monkey wrench. As stated above, eat better and move. That’s how results come.
3500 cals always equal a pound as in 3 feet always equal a yard. Burning off those calories, more accurately, is a function of a well heated metabolism vs a sluggish metabolism brought on by a number of factors. This is one reason why increasing muscle mass while dieting is so important. Some books go onto to say that you shouldn’t even boter dieting if you don’t plan on exercising. No blanket statment applies. Everybody is unique with a variety of challenges. If you wnat to lose weight, change your lifestyle gradually to one you can be happy with for the years you have left.
Feet and yards are both measures of distance and by definition their relationship to each other is fixed.
Calories are a measure of energy and a pound is a measure of weight. Without specifying many other factors, they do not have an inherent relationship.
Your analogy is heavily flawed.
And no, e=mc^2 does not count here. :P