How many calories are in a pound?

This seemingly simple question stumped me on my family medicine board recertification exam seven years ago — twice. (I think they asked the question in two different ways. I hoped they were experimental questions that didn’t count.) Later that day, I found the answer: 3,500 calories equals one pound.

I don’t remember which multiple-choice answer I chose, but I do remember choosing the same answer both times.

It’s a measurement we take during almost every patient encounter. Why didn’t I remember this simple value?

I didn’t remember ever learning it.

I realized that when we are growing, the questions are always: Are we getting enough calories? Is your three-month old following the growth curve while breastfeeding? Is she getting the recommended 90-100 calories/kg, if you use formula? There are general guidelines for calories/kg for age groups, but we track progress by periodic weighing and feeding to stay on a curve. Yet, few of us pay much attention to how our eating habits and activity levels affect our weight — until we weigh too much.

Then we ask, “How many calories are in a pound?”

I describe to my patients that if at the end of the day you take in 3,500 calories more than you burn off, you will gain one pound. Therefore, the opposite is also true. My patients seem to get this.

I rationalize that they do not need to choose a grapefruit-only diet or exercise five hours a day to successfully lose weight. Rather, small, sustainable changes can be effective. A decrease in 250 calories per day can lead to a loss of one pound in two weeks. That’s two pounds a month — give or take holidays, restaurants and occasional lapses — resulting in 10-to-12 pounds per year. This pace of weight loss would be realistic and great. We typically gain weight slowly over many years, so we can lose it slowly, too.

I often hear the rebuttals of: “I eat a super healthy diet!” “I must walk at least five miles a day at work!” “I don’t know where the weight is coming from!” I point out that if the adult growth curve shows a steady increase, despite the super healthy diet or miles walked at work, something still has to change if you are going to expect results.

A change in portion size at dinner, not going back for seconds and trading the super-mega-big-gulp of soda for water can all be great starts. Increasing your activity by scheduling blocked out time to walk at lunch, increasing your forty-five minutes on a treadmill to sixty and adding a day of activity each week can also help.

But there are those who challenge the idea that if you burn 3,500 calories you will lose one pound of fat. In fact, some models suggest that over time, as your body adapts to your efforts to lose weight, it may actually require closer to a 7,000-calorie deficit to equal one pound of weight loss. This is fine and actually comes closer to my projected 10-to-12-pound weight loss in a year. It still reinforces that progress is made once patients start to fundamentally change.

When I see that a patient has been successful in weight loss, I ask him how he did it. More often than not, the response is “You said to eat less and exercise more. So I did.” Many of my patients trend down slowly over time.

I love the great success stories. For example, one patient returned after a year and was eighty pounds lighter. To celebrate his accomplishment, he wore the same pants from a year before but used a rope as a belt to hold them up. His success came from starting to ride his bike to work, decreasing his portion sizes and cutting soda.

I find that we tend to underestimate our true daily caloric intake and overestimate our expenditures. So while burning a pound of fat in a calorimeter, as was done in 1953, gave us our value of 3,500 calories in a pound, working toward sustainable dietary and activity changes can help us reach realistic goals.

Ted Paisley is a family physician who blogs at Family Medicine Vital Signs.

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