How many times have you heard this? If you eat 500 calories less per day, since one pound of weight equals 3500 calories, you’ll lose one pound a week. “Untrue!” say researchers studying weight and metabolic rate.
Unfortunately, despite published research pointing out the inaccuracies of these predictions, it’s clear that word has not gotten out to most people, including many health professionals. In today’s Smart Bytes®, I’m sharing a video interview with an acclaimed researcher who explains the situation. Following the video, read on for a link to a calculation tool that much more accurately estimates weight changes in response to changes in your eating habits.
The expert I recently had the chance to interview is Steven Heymsfield, MD, Executive Director of the Pennington Biomedical Research Center and an internationally renowned expert on research on this topic. Dr. Heymsfield was speaking at the latest symposium sponsored by SCAN (Sports, Cardiovascular and Wellness) dietetic practice group, a specialty unit within the Academy of Nutrition and Dietetics.
(Email subscribers, click to go to the Smart Bytes® blog to watch.)
The 3500 Calorie Rule & Its Misuse
The idea that 3500 calories convert to one pound of weight is based on experiments published in 1958, was known as “Wishnofsky’s Rule”, named after researcher Max Wishnofsky. Ask anyone who studied college-level nutrition anytime from 1960 up until very recent times, and you’ll hear the “3500 Calories equal a pound” rule recited as something written in stone. Here are some of the ways you may have heard this used, all of which were originally considered correct, but have now been proven inaccurate:
- Cut 500 calories a day from your current eating habits and you’ll lose a pound a week.
- If you don’t want to cut 500 calories a day from your eating, use a combination of reducing calorie consumption and burning more calories in exercise to create this 500 calorie “gap”, and you’ll still lose a pound a week.
- If you make small changes to cut even 150 calories a day, that will add up to 15 pounds of weight loss after one year. (Based on this math: 150 calories cut x 365 days = 54,750 calories cut over a year, and 54,750 calories divided by 3500 calories/pound = 15.6 pounds lost.)
- Every little bite you overeat matters: just 50 calories extra a day adds up to a 5-pound weight gain each year. (Because it adds a total of 18,250 extra calories a year, which when divided by 3500 calories/pound equals 5 pounds)
Yes, working on the best information available at the time, until just a few years ago, I’ve been among the many well-meaning people giving advice based on that equation.
Why the “3500 Calorie Rule” Doesn’t Work
The 3500 Calorie equation was developed based on a relatively limited group of subjects in short-term studies (never based on long-term outcomes), and using research practices current at the time that did not have the advantage of today’s astonishing computer-generated calculation models.
When researchers today track changes in weight, calorie consumption and calorie-burning, by far the majority of people lose less weight than expected using the 3500 Calorie Rule.
Why is a rule-of-thumb that was so widely accepted now seen as obsolete? Here are a few major reasons:
- Individual differences in basic metabolic rate: We are not all the same in the basic calories we burn just keeping our body functioning. Differences in age, height, weight and body composition all play out in differences in metabolic rate. For example, a person who weighs more burns more calories all day long doing the same things as a person who weighs less. Cutting 100—or 500 – calories a day will impact different individuals differently.
- Metabolic adaptation: Even within the same individual, the same cut in calorie consumption changes over time in the weight loss it produces. In part, this is a reflection of the above – as you weigh less, you burn fewer calories all day doing the same things; so continuing the same change in eating habits will show up as slower and slower weight loss over time. Researchers continue to study what else this metabolic adaptation may involve.
- Unseen differences in activity: Another small but important part of the calories we burn in activity is not the “big stuff” of taking a walk, climbing the stairs or mowing the lawn. Very small bits of activity add up, too. Sometimes people make changes in the activities of daily life without realizing it, and that feeds into how much weight loss occurs, too. Some are foot-waving, finger-drumming people who can’t sit still; others can comfortably sit for hours without moving.
What to Do?
If you’re looking at changes in eating choices and physical activity you can make that would lead to weight loss, the idea of cutting 250 to 500 calories a day is still a reasonably good target for many people.
- Just don’t set your expectations on those changes leading to weight loss of a half-pound or pound a week, respectively. Remind yourself that you’re in this for the long-run. Watch for changes in areas other than weight that often show up faster than weight loss itself. For example, you might track blood pressure or even your energy level.
- If your weight is currently very high or your calorie consumption is far, far beyond what you need, you might reasonably be able make cuts in calorie consumption beyond 500 calories a day. But if such large cuts would bring your total calories so low that you don’t have room for the foods you need to meet your nutrient needs, or would be changes too dramatic for you to feel comfortable and not deprived, then pushing for huge calorie cuts is likely not worth the challenges it would pose. This is most certainly something you’d need to discuss with your personal physician.
Researchers have developed a new model – known as the Dynamic Model — for predicting weight loss based on changes in calorie consumption. Since it includes multiple influences and factors in observed metabolic adaptations along the way, using this model requires advanced computer-dependent calculations.
It’s not as simple as the “3500 calories equals a pound” concept so many of us have carried in our heads for years. But the researchers involved have made the model available as “apps” that can be downloaded free of charge. You can enter in your age, height, weight and gender, and for any specific time period, the app will give you a prediction of how weight will change over time for any specific total calorie consumption or change in calorie consumption (up or down) that is far more accurate than what we’ve had available previously.
Here is the link where you can download the app developed by Diana Thomas, PhD, and her colleagues so you can run the Dynamic Model on your computer. Follow the instructions there, and note that you will need to enable macros for the program to work. (Note: link below is an updated URL as of January 2016.)
Still, remember that we are all individuals, and no model is perfect. Focus on making smart and healthy changes in your eating and activity choices. If the results seem to be off-track, it can be an opportunity for a reality check as to whether you are consistently doing what you think. If you are, then keep your focus on the lifestyle you want to create and don’t panic.
Check back for the next portion of my video interview with Dr. Heymsfield, in which we discuss key information about how calorie balance and weight changes with increasing age and with physical activity.
Hall KD et al. Energy balance and its components: implications for body weight regulation. (American Society for Nutrition Consensus Statement). Amer J Clinical Nutrition. 2012; 95:989–94.
Thomas DM et al. Can a weight loss of one pound a week be achieved with a 3500-kcal deficit? Commentary on a commonly accepted rule. International Journal of Obesity, advance online publication April 30,2013. doi: 10.1038/ijo.2013.51
Casazza K, et al. Myths, presumptions, and facts about obesity. N Engl J Med. Jan 31, 2013; 368(5):446-54.
Hall KD. Predicting metabolic adaptation, body weight change, and energy intake in humans. Am J Physiol Endocrinol Metab. 2010 Mar;298(3):E449-66.