November 2014 Issue

Farewell to the 3,500-Calorie Rule
By Densie Webb, PhD, RD
Today's Dietitian
Vol. 26 No. 11 P. 36

Researchers have developed new mathematical formulas RDs can use to more accurately predict the rate of weight loss in patients.

If you've counseled clients and patients for weight loss, you know that even the most diligent of dieters eventually will reach a weight-loss steady state, a plateau, a stumbling block that can be frustrating for them and dietitians alike. And, unfortunately, a large percentage of those who succeed at losing weight will gain it back over time.

We all know the weight-loss rules: eat more calories than you burn and you'll gain weight; eat fewer calories than you burn and you'll lose weight. However, researchers say it's not that simple. In an effort to better understand the weight-loss process, researchers have devised an ingenious way to more accurately predict the trajectory of weight loss for individuals via a mathematical formula. The hope is that using it will result in more realistic expectations for weight loss with fewer disappointments along the way, and help explain when and why weight-loss plateaus occur, even among seemingly dedicated dieters.

Also in development is a personalized dynamic feedback control mechanism that clients can wear to monitor their progress and determine when it's time for reassessment with a dietitian. It's also a method for RDs to predict in advance who's most likely to succeed at losing those excess pounds longterm.

Conventional Weight-Loss Wisdom
Ask any dietitian and he or she likely will say that cutting food intake by 3,500 calories results in a 1-lb loss. Cut 500 calories per day and that's 1 lb per week. Over the course of one year, that would equal 52 lbs. That's what RDs have been and continue to be taught, and it's promulgated by the US Surgeon General and the Academy of Nutrition and Dietetics, and it's repeated in several nutrition textbooks.

It's been estimated that the 3,500-calorie rule is cited in more than 35,000 educational weight-loss sites.1 In September, the Journal of the American Medical Association published a patient handout titled Healthy Weight Loss, in which the first sentence states, "A total of 3,500 calories equals 1 pound of body fat. This means if you decrease (or increase) your intake by 500 calories daily, you will lose (or gain) 1 pound per week."2 Undoubtedly, the 3,500-calorie dogma still is being taught even though it's been shown that it simply doesn't work this way. So where did the 3,500-calorie weight-loss wisdom come from? It originated from researcher Max Wishnofsky, MD, in 1958, who calculated that 1 lb of fat stores approximately 3,500 kcal of energy.3 It was appealingly simple, and it stuck.

"I think this happens often when there is a simple rule of thumb," says Diana Thomas, PhD, director of the Center for Quantitative Obesity Research at Montclair State University, and one of the researchers involved in developing the new approaches. "It's easy to propagate, and there's resistance to adopting something that's more complex."

The 3,500-calories-per-pound rule seemed to make sense at the time, but much has occurred in the area of human nutrition in the last 55 years, including the sharing of expertise among fields. The breakthrough in the understanding of how and why weight loss occurs and predicting the rate at which it does, is the result of experts in nutrition and mathematics putting their collective heads together, coming up with complex formulas and then simplifying them.

Elusive Weight-Loss Success
The experts Today's Dietitian spoke with agree that while the 3,500-calories-per-pound rule does seem to work fairly well in the short term and for those who want to lose only a few pounds, the logic begins to fall apart over the long term, especially for those trying to lose a significant amount of weight. Dietitians know that as an individual loses weight, the body's energy requirements decrease, but the dynamic physiological adaptations that occur never have been quantified or figured into the 3,500-calorie rule.4 The most serious error of the 3,500-calorie rule is its failure to account for dynamic changes in energy balance that occur during a dieting intervention.5 Also not taken into account: gender, the fact that eating and exercise habits may change over time, and poor compliance, all of which can affect weight loss. Because of this, the experts say, the 3,500-calorie-per-pound approach significantly overestimates how much weight people will lose over time, setting them up for disappointment when weight loss slows or stops altogether.1 In other words, the body adapts and lifestyles change in myriad ways that minimize or even eradicate the impact of reduced calorie intake and, until recently, there has been no way to predict how consuming fewer calories may affect the rate of weight loss among individuals trying to lose weight, especially when the goal is to lose more than just a few pounds.

The new complex weight-loss formulas factor in the drop in metabolic rate that occurs over time as body mass decreases. After applying the formulas to individuals, a main conclusion Thomas and other researchers have drawn isn't a popular one—that people generally plateau early in the weight-loss process, not because of a metabolic slowdown, although that does occur, but because they don't adhere to calorie-reduced diet plans consistently long term.4,6

"If a plateau is reached within six months, then in all likelihood, the person is no longer strictly adhering to the diet," says Carson C. Chow, PhD, a senior investigator in the mathematical biology section of the National Institutes of Health (NIH). Six to nine months is the typical timeline for dieters to reach the dreaded plateau, but "given that body weight changes so slowly, it could be stretched out to a year," Chow says. The new formulas allow clinicians to see what realistically can be expected based on the individual's weight, age, gender, and physical activity, and close monitoring allows for adjustments in the predictive formula.7

Where exactly does exercise fit in? The effect of physical activity on the rate of weight loss isn't clear. However, research suggests that the small amount of weight loss sometimes seen in exercise intervention studies isn't due to exercise's lack of effect on weight loss, but it's a result of not getting enough exercise prescribed,6 and that's compounded by an increase in calorie intake—in other words, not sticking to the prescribed reduced-calorie diet long term.1 The ratio of macronutrients in the diet, specifically the ratio of protein to carbohydrates and fat, has been endorsed as a way to promote weight loss. However, little effect has been demonstrated in the short term.

Yet, according to Kevin Hall, PhD, a senior investigator in the mathematical biology section of the NIH, not enough is known about the long-term effects of varying macronutrient diet composition.4 As a result, the ratio of macronutrients in the diet isn't included in the new weight-loss prediction formulas.

New Weight-Loss Math
To access the programs and apps for assessing the weight-loss trajectory of clients and patients, Hall and colleagues at the NIH have developed the Body Weight Simulator, available at At first glance, it may not look that different from other weight-loss predictors, but a tremendous amount of mathematical calculations have gone into its development. Plug in your client's information (weight, height, activity level, goal weight, length of time to reach goal) and it will provide a calorie level for weight loss and a calorie level for maintenance. Thomas and her colleagues at Pennington Biomedical Research Center in Baton Rouge, Louisiana, also have developed a Single Subject Weight Change Predictor application for predicting weight loss, which can be found at Using the Pennington online calculator, a 200-lb man aged 35 who cut 500 kcal/day from his diet would be expected to lose 23 lbs in one year vs 23 lbs in four months in accordance with the 3,500-calorie-per-pound rule.

Hall and Thomas agree that while there are several minor differences in their models, the predictions are similar. The NIH calculator allows for more detailed input about physical activity, and the Pennington model enables users to compare the newly calculated downward weight-loss trajectory, based on your input, with that of the 3,500-calorie-per-pound rule.

The new mathematical approaches have been validated repeatedly, researchers say. In fact, the 3,500-calorie guideline was refuted in a consensus statement issued jointly by the American Society for Nutrition and the International Life Sciences Institute in 2012,8 although the math approaches haven't been widely adopted for clinical weight management or used to inform policy discussions.4 Still, Hall has high hopes for the new weight-loss math.

"I think our methods could be used to remotely monitor patients and detect early signs of adherence loss that would trigger a counseling session or a reevaluation of weight goals and the type of intervention," says Hall, who has invented the personalized dynamic feedback control device, for which the NIH has filed a patent.9 No word on when or if it will be available, but it looks like it may be the way of the future.

If clients and patients prefer something less complex, Chow has broken it down to a simple rule of thumb. "While the 3,500-calorie rule has been challenged in the past, we were the first to replace it with an equally simple, but more accurate rule, and that is that 'every 10 calories per day decrease in calorie intake leads to an eventual one-pound loss,' but it can take three years to get there," Chow says. In other words, weight loss isn't a linear event over time, as the 3,500-calorie rule suggests. All of this new information shows that weight loss may be slow, even slower than we thought. That makes patience a major factor in weight-loss success. And because compliance wanes over time, consistency is the other major part of the equation that adds up to successful weight loss.

"Successful weight management is a long-term endeavor that requires diligence each and every day," says Corby Martin, PhD, director of the Ingestive Behavior Laboratory at Pennington Biomedical Research Center. "It's critical that patients and dietitians continuously monitor progress and adjust their treatment strategy accordingly. If a patient's current treatment regimen isn't working, it's imperative to detect this as early as possible and employ more intensive strategies." Both Chow and Hall believe that taking active control of food consumption may be required to limit the long-term increase in energy intake that typically occurs, especially in the face of the dramatic rise in availability and marketing of highly palatable, convenient, inexpensive, and energy-dense foods.7

And perhaps most intriguing is the new research expected to be published this year by Thomas and colleagues. "We have a paper under review about a way to make it easy for dietitians to identify, from short-term data, who's likely to be successful at losing weight over the long term."

Counseling Recommendations
The 3,500-calorie-per-pound rule is dead, or it should be. In its place are new online tools to help RDs better predict how much weight clients and patients realistically can expect to lose over time. In addition, Martin believes the new mathematical formulas can inform dietitians when it's time to reevaluate their clients' or patients' progress and help them decide what realistic adjustments are needed. If weight-loss milestones haven't been reached, then it may be time to reassess what the client is or isn't doing. Martin recommends weekly or biweekly check-ins to see how clients are doing. More thorough reviews of progress, he says, should occur every three to six months.

While the new online tools likely will predict much slower progress than anyone would like, dietitians can use them to help clients and patients set more realistic goals and let them know that progress probably will be slow and unsteady. Furthermore, if they've been reading about weight loss online or in diet books, inform them that the thinking has changed dramatically and the 3,500 calories-per-pound rule no longer applies.

— Densie Webb, PhD, RD, is a freelance writer, editor, and industry consultant based in Austin, Texas.

1. Thomas DM, Martin CK, Lettieri S, et al. Can a weight loss of one pound a week be achieved with a 3500-kcal deficit? Commentary on a commonly accepted rule. Int J Obes (Lond). 2013;37(12):1611-1613.

2. Guth E. JAMA patient page: healthy weight loss. JAMA. 2014;312(9):974.

3. Wishnofsky M. Caloric equivalents of gained or lost weight. Am J Clin Nutr. 1958;6(5):542-546.

4. Hall KD, Sacks G, Chandramohan D, et al. Quantification of the effect of energy imbalance on bodyweight. Lancet. 2011;378(9793):826-837.

5. Hall KD, Chow CC. Why is the 3500 kcal per pound weight loss rule wrong? Int J Obes (Lond). 2013;37(12):1614.

6. Thomas DM, Bouchard C, Church T, et al. Why do individuals not lose more weight from an exercise intervention at a defined dose? An energy balance analysis. Obes Rev. 2012;13(10):835-847.

7. Chow CC, Hall KD. Short and long-term energy intake patterns and their implications for human body weight regulation. Physiol Behav. 2014;134:60-65.

8. Hall KD, Heymsfield SB, Kemnitz JW, Klein S, Schoeller DA, Speakman JR. Energy balance and its components: implications for body weight regulation. Am J Clin Nutr. 2012;95(4):989-994.

9. Personalized dynamic feedback control of body weight: United States patent application US 20130198214 A1. Google Patents website. Accessed September 4, 2014.