For anyone who’s been on a diet or attempted to lose weight in the past 30 years, a familiar piece of advice went something like this: “A pound of fat contains about 3500 calories. Simply subtract 500 calories per day from what you’re eating, which will create a deficit of 3500 calories over one week (500 calories/day x 7 days = 3500 calories). You’ll lose a pound each week and lose 52 pounds in one year!”
It sounds really simple. And the math is right, a pound of fat contains about 3500 calories. But there are several reasons why this line of thinking is misleading.
The first thing to consider is that metabolism changes as weight loss occurs. Consider this example: a 40 year-old, mostly sedentary, 250 pound, 5’8” male needs around 2400 calories per day to maintain that weight (on average). His goal is to get back to around 190 pounds, where he was at before he became sedentary and started eating poorly. Let’s say this individual starts eating around 1900 calories per day. He should, theoretically, lose around a pound a week for a while.
But let’s say he’s lost 40 pounds, putting him around 210 pounds. His body now needs around 2100 calories per day to maintain his new weight. If he’s still following the same plan, he will no longer be losing a full pound every week.
At this point, many people become frustrated and either give up on the changes they’ve made or totally change their approach. What they don’t realize is that they may still be moving towards their goals, simply at a slower rate than they initially did. That’s okay. Slight adjustments can be made, but patience is important in achieving and sustaining weight loss. Sometimes plateaus are even a part of the process.
The wrong thing to do in this scenario is to continue progressively cutting calories until you reach a restrictive level (let’s say 1400 calories in the above scenario). By doing so, inevitably you will reach a point where your body, in a deprived state, starts pulling energy from muscle tissue and drastically slowing metabolism. This is a recipe for eventual weight re-gain and sets the individual up for weight cycling, which isn’t good news for your health.
Gradual weight loss is okay, and allows you to utilize lifestyle changes that you can keep at the end of the process rather than asking yourself “I can’t starve myself anymore…now what?”
The National Institute of Health has developed a more realistic simulator for weight loss that accounts for metabolism changes, and gives you feedback if you set goals that are unrealistic in a certain time frame. It’s not a perfect model, but that doesn’t exist. Follow this link to see the NIH “Body Weight Planner.”
Some other problems with the 3500 calorie rule of weight loss include:
Inaccurate calorie counting. We have more nutrition information available than ever, but it’s still very difficult to accurately estimate portions and calorie counts. In most studies, people consistently underestimate their calorie intake. This is compounded when we account for calories burned during exercise, which can also be difficult to accurately determine.
The starting point is wrong. If an individual has been gaining weight and cuts 500 calories per day, that may only mean that they will now maintain their weight or gain weight more slowly than they have been.
Not everyone wants to (or should) count calories. There are other strategies to lose weight outside of counting calories every day. In fact, many people do better on plans that do not involve calorie counting, which can be time-consuming, confusing, and can feed into anxiety and perfectionism around food which are detrimental and unnecessary.
For more great information on this topic, check out quality articles written by registered dietitians here and here.