Wednesday, February 27, 2013

Calculation Errors: Predicting Weight Loss or Gain With Calories

You can't predict an exact weight loss or weight gain by using calories.

A pound of pure fat consists of 3,500 calories. Many exercise and nutritional professionals know this because their weight loss formulas operate on this fact. Even if you add or subtract 500 calories per day, it's extremely unlikely that you will have added or subtracted a pound of fat in one week.

Don't believe me? Look at the research.

Adding Weight

A study at Laval University in Quebec, Canada, looked at weight gain as a result of overfeeding [1]. In this study, 24 men between 19 and 27 years old were overfed 84,000 calories in a span of 100 days. The men were essentially contained in a dorm unit for 120 days, which includes time for pre- and post-tests. During the pretesting weeks, the researchers averaged the men's typical daily calorie intake and expenditure.

During the test period, all meals were prepared by dieticians to be as calorically accurate as possible. The men were not allowed to exercise, other than to take a half hour walk per day. In other words, calories "burned" through physical activity were minimized and controlled. When the researchers calculated the excess calories, they accounted for the energy expended by the men during their usual activities.

If you do the math, 84,000 divided by 3,500 (the amount of calories in a pound of fat) translates to a 24 lbs - all men should have gained 24 pounds. Also, if the calorie formula is correct, all men should gain the same amount of weight.

But neither are true. The average weight gain was 17.8 lbs. The weight gain ranged from 9.5 to 29.3 lbs.

Adding further confusion to the calorie formula, the 24 men were 12 pairs of identical twins. The weight gain correlation between twins was much greater than the correlation with other participants. This means that genetics influences how much of our excess intake is stored as fat.

Losing Weight

Researchers at the University of Leeds in England studied the effects of a calorie deficit via exercise on obese and overweight men and women [2]. The participants were provided specific recommendations for expending 500 calories per workout through aerobic activities such as cycling or rowing. They exercised five days per week for 12 weeks.

While the researchers did not perfectly control participant food intake, they did measure the participants' intake when eating freely before the test period and provided meals of the same calorie content and macronutrient breakdown before follow-up tests. Assuming a constant intake, the weight loss over the 12 weeks should equal 8.6 lbs.

The weight loss was actually close at 8.1 lbs, but the change in weight ranged from a loss of 32.3 lbs to a GAIN of 3.7 lbs! Imagine gaining 3.7 lbs after 12 weeks of aerobic exercise...ouch.

The Confounding Factors

As you see in the overfeeding study, genetics plays a role in how much of the excess food is stored. Another explanation for the variation in weight changes is non-exercise adaptive thermogenesis (NEAT). NEAT are the calories expended when not physically active or sleeping. For example, some people expend a lot of calories by simply fidgeting around over the course of the day, whereas other people fidget very little. The difference in NEAT from a "fidgeter" to a "non-fidgeter" can be hundreds of calories per day. A third reason is the change in types of tissues. During both studies, changes in lean mass (muscle, bone, and other organs) versus fat mass varied greatly from person to person.

The studies discussed are not perfect by any means. The overfeeding study is more controlled than the exercise study, but it's possible calorie estimates were not perfect for the food provided to the men who were kept in the dorm unit.

However, even if the studies were controlled even further, factors such as genetics and NEAT influence how each person acts on calorie deficits and surpluses. Predicting weight changes via calorie equations is a waste of time. A more constructive route is simply making lifestyle changes one at a time while studying their individual impacts on feedback measures (i.e. the scale, measurements, body composition tests).

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