How Many Calories Equal One Pound?
By Densie Webb, PhD, RD
The New Consensus Statement Questions Weight-Loss Dogma
Dietitians and dieters alike have long portrayed weight management as a simple matter of calories in vs. calories out. Eat more calories than you burn, and you’ll gain weight. Burn more calories than you consume, and you’ll lose weight.
The magic number of calories bandied about for decades has been 3,500—subtract that number from your diet or burn off 3,500 calories more than what you consume, and you’ll lose 1 lb.
But a panel of experts, convened by the American Society of Nutrition and the International Life Sciences Institute, recently developed a consensus statement on the subject, “Energy Balance and Its Components: Implications for Body Weight Regulation,” which questions the 3,500-kcal rule along with several other long-held convictions about energy balance and weight loss. While the panel was charged with answering pertinent questions about weight management, it concluded that many of the body’s methods for gaining, losing, or maintaining weight remain a mystery.
Here are some of the concepts the new consensus statement addressed:
• 3,500 kcal = 1 lb: According to the consensus panel, this rule of thumb is an inaccurate predictor of weight change and should no longer be used. The 3,500-kcal/lb rule assumes that body weight changes linearly over long periods of time, which isn’t the case. As an individual loses weight, resting energy expenditure drops due to less body mass (not a “slow metabolism,” as often assumed).
New weight-loss prediction formulas have been developed that take this reduced energy expenditure into account and offer a much slower, but more realistic, weight-loss rate that patients and clients can expect with sustained changes in energy intake and output. The complex formulas have been simplified and are available at www.pbrc.edu/the-research/tools/weight-loss-predictor and http://bwsimulator.niddk.nih.gov.
By typing in an individual’s information (height, weight, age, current calorie intake, calorie reduction, activity level), a weight-loss prediction table is produced. The panel suggested that the online formulas, or something similar, should replace the 3,500-kcal/lb rule.
“What we’re trying to do with the new formulas is to get people to think in a fundamentally different way about calories and energy balance,” says John R. Speakman, PhD, of the University of Aberdeen in Scotland and one of the consensus statement authors.
• Weight loss over time: No well-controlled study in metabolic wards where subjects’ diets are carefully monitored and blood, urine, and fecal samples are collected (the only way to accurately measure energy balance) can be conducted for an extended period of time, leaving unanswered questions regarding long-term energy balance. Based on recent analyses, however, reducing calorie intake by 500 kcal/day should result in an approximate 25-lb weight loss over one year, with another 22-lb loss over three years, in contrast to the current 3,500 kcal-per pound rule, which estimates a much more generous 52-lb weight loss in one year. “You have to consider the time element,” Speakman says.
• Carbohydrates, protein, and fat: It’s the first lesson in Nutrition 101—carbohydrates and proteins provide 4 kcal/g, and fats provide 9 kcal/g. What’s seldom mentioned, however, is that these numbers represent population averages of energy that food provides the body. These numbers don’t accurately reflect the calories produced by individuals from these macronutrients. The actual calories available for energy are influenced by several factors, including an individual’s gut flora, the way the food is prepared, how well the food is chewed, and the overall diet composition.
Currently, there’s no way to determine how much energy an individual actually obtains from 1 g of carbohydrate, protein, or fat. The 4/4/9 calorie rule is all we have to go by, but as dietitians, it’s important to keep in mind that the numbers don’t always reflect reality from individual to individual.
• Exercise: According to the consensus statement, exercise can produce wide variations in body weight response, with some people losing significant amounts of weight and others actually gaining weight. The expert panel suggested that part of the variability in weight change may not be due to differences in the body’s response to exercise but how individuals compensate for exercise with increased food intake. “This compensation,” Speakman says, “makes it even harder to generate a large calorie deficit.”
Small Changes = Big Results?
In the last several years, “small changes” has become the battle cry against weight gain. If cutting back significantly on calorie intake or exercising daily for long periods is too difficult, the answer, some experts say, is to make small changes that add up to significant weight loss over time. The 3,500-kcal/lb rule has been used to model the effects of small changes and, therefore, the panel says, has generated unrealistic expectations about how much weight one can lose over time.
For example, using the 3,500-kcal/lb rule, a small 40-kcal/day reduction in energy intake would result in a 20-lb weight loss over five years. However, using the new predictive equation, that 40-kcal/day reduction would result in only a 4-lb weight loss over the same period. In addition, according to the consensus panel, a tremendous amount of error is built into assessments of calorie intake and expenditure, so much so that, according to the panel, this error easily can reach 1,000 kcal/day, making it nearly impossible to estimate the effect small changes will have on weight loss over time.
While many issues about energy balance and weight management remain unresolved, one simple truth has emerged from the new consensus statement: The 3,500-kcal/lb rule no longer applies and, as dietitians, we need to reevaluate our weight-loss advice to clients and patients and offer more realistic projections about weight loss.
— Densie Webb, PhD, RD, is a freelance writer, editor, and industry consultant based in Austin, Texas.