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“This research helps us understand why one person may lose weight faster or slower than another, even when they eat the same diet and do the same exercise.”
 Kevin D. Hall, PhD, Science Daily, August 26, 2011

Weight Loss Is a Dynamic Process

Results Vary Based on Diet, Activity, Body Composition, and Time

Government budget projections are notoriously inaccurate, because they use static analysis. For example, they assume that a 10 percent tax increase will produce 10 percent more revenue. It almost never works out that way. People are dynamic; they change their behavior when taxes go up. Tax something and you almost always get less of it. Diets are the same. They almost never work out as planned. Our bodies react to energy deficits, created by dieting or exercise, in different ways.

Researchers at the National Institutes of Health have created a mathematical model of what happens when people of varying weights, diets, and exercise habits try to change their weight. The results have the potential to change our perspective on weight control. The more we understand about the process, the more realistic we are, the happier we’re likely to be with our results. Aligning reality and expectations will make us better managers of our bodies.

To test and fine tune the model, the researchers compared predicted weight changes to actual changes in people. The results are reported in an issue of Lancet devoted to obesity (August 27, 2011). The report, authored by Kevin D. Hall, PhD, and colleagues, is titled “Quantification of the effect of energy imbalance on bodyweight.”

Several important insights have emerged: 1) Steady weight loss is a myth: 2) Heavier people respond faster to diet change than people with less initial body fat; and 3) We can predict the effect of a single permanent change in diet or exercise for the average overweight person.

Myth Exposed

The fundamental principle of bodyweight change is that you must tip the balance between energy intake and expenditure. Tip it one way and you gain weight and tip it the other you lose weight. What could be simpler than that? Sounds straightforward; unfortunately, it’s not.

The widely quoted 3500 calories per pound rule is a well-meaning myth. “This ubiquitous weight loss rule was derived by estimation of the energy content of weight loss [3500 calories in a pound of fat],” Hall et al wrote, “but it ignores dynamic physiological adaptations to altered body weight that lead to changes of both resting metabolic rate as well as the energy cost of physical activity.” Put another way, negative calorie imbalance—through diet or exercise—causes the body to slow down and operate more frugally.

While it is generally recognized that the static weight loss rule is simplistic, little has been done to measure how diet and exercise translate into weight loss over time. Hall and his team address this issue by using a mathematical model that incorporates our knowledge of how the human body responds to changes in diet and physical activity. “We show how this dynamic simulation model of human metabolism can predict the time course of weight change at both the individual and population level,” Hall et al write.

Let’s look at the key messages.

Body Composition

Body fat contains about five times more energy (calories) than lean tissue. That affects the dynamics of weight loss. People with a higher proportion of body fat lose body weight at a different rate than those with a lower percentage of fat. “People with a higher initial adiposity partition a greater proportion of a net energy imbalance towards gain or loss of body fat versus lean tissue than do people with low initial adiposity,” the Hall team wrote. In short, a greater proportion of weight loss is fat for people who start out with more fat. Moreover, as you become leaner the rate of fat loss slows down.

While the underlying mechanism is complex and not fully understood, we’ve know the outcome for many years. “The net result can be described by a simple equation first presented more than 30 years ago and subsequently updated and validated,” the researchers tell us.

Importantly, lean tissue is more active and burns more energy. Lean tissue “contributes more to the body’s energy expenditure rate,” Hall et al relate. Muscle is more expensive to build and maintain than fat—and is protected accordingly. The energy expenditure differential is apparent in the resting metabolic rate and the energy cost of tissue deposition and turn over, according to the report. Lean tissue is more active than fat tissue around the clock, 24-7.

Importantly, the relative value of lean and fat tissues is dynamic; it changes as weight loss progresses. As the body becomes leaner, fat becomes more important for survival and the value of lean tissue declines.

These factors have been incorporated in a mathematical model of human metabolism and body composition change for adults. Close agreement between the model and weight loss studies provide validation of the mathematical model, according to the researchers. Notably, the data from these studies was not available when the model was being developed; in short, the model has stood the test of time.

Dynamic Simulation Model

A complicating factor is that it’s difficult to measure the initial energy requirement of free-living individuals. “This is a fundamental limitation on our ability to precisely calculate the predicted bodyweight time course of an individual,” the researchers warned. That would almost always be true for people dieting on their own, which would include most people embarking on a weight loss regimen. Understanding the factors involved is quite helpful nevertheless.

We start with the assumption that changes are from a neutral energy balance; energy intake and expenditure are in balance.

The Hall et al report includes a predicted bodyweight time course for a 220-pound sedentary man cutting calories by a steady 480 per day. “This constant diet perturbation (change) was predicted to result in a bodyweight plateau at about 165 pounds over a 10-year simulation taking roughly 1 year to reach half of the maximum weight loss and reaching 95% of this value after about 3 years,” the Hall team wrote.

As noted earlier, steady weight loss is a myth. The popular diet rule (3500 calories per pound) would predict that a steady daily 480-calorie reduction would result in a loss of 48.5 pounds in the first year, which is almost 100% greater than the model would predict.

Under the model, half of the loss occurred in the first year; the rate of loss then slowed by half over the next two years. (That would be a good thing to know at the one year point.) At three years, the calorie intake and expenditure came into balance, causing weight to plateau over the final seven years. Keep in mind that the model reflects a single permanent change in diet (or exercise).

It probably wouldn’t happen precisely this way in real life, but the general course should be roughly the same. For one thing, perfect adherence is most unlikely.

As noted earlier, body composition would also make a difference. Adults with a higher—or lower—percentage of body fat would be expected to lose more—or less—weight for the same reduction in energy intake.

A fatter man might go down to 155 pounds and take more than three years to get there. A leaner man might plateau at 175 pounds, because the energetically expensive lean tissue mass is preserved.

Keep in mind, too, that the bodyweight time course is dynamic; it changes as the fat-to-lean ratio changes. As the body becomes leaner, fat becomes more important for survival and the value of lean tissue declines. It’s a little complicated, but you get the idea. The leaner you because, the more difficult it becomes to lose fat.

Diet versus Exercise

What about physical activity? Does an increase in physical activity necessarily lead to the same weight loss as an energy-equivalent decrease in food intake? Not necessarily, according to the researchers. Again using a 220-pound sedentary overweight man, the Hall team compares cutting calories by 480 per day with increasing activity by a like amount (exercise).

“Such a relatively modest increase of physical activity results in slightly more rapid and greater predicted weight loss compared with an energy equivalent reduction of food intake,” Hall et al write. “However, as the magnitude of each intervention increases, there is a point when diet leads to greater weight loss than does physical activity.” That’s because the energy expenditure of added physical activity is proportional to bodyweight itself, the researchers explain. As bodyweight goes down a fixed amount of exercise burns fewer calories.

“Therefore, by contrast with the assumption that a calorie is a calorie with respect to physical activity, our model shows that energy-equivalent initial changes in physical activity versus food intake can lead to differences in weight change, but experimental confirmation of this would be difficult.” (Emphasis mine)

Again, it’s complicated. The take away message, I believe, is that a slight decrease in calories combined with a slight increase in physical activity is the best plan. It’s easier on you and doesn’t set off metabolic alarm bells in your body. As I wrote in Ripped 3, bigger changes in calories or activity “defeat your purpose in three ways: 1) your metabolism slows down to save energy; 2) you lose muscle tissue; and 3) you get hungry and binge.”

Let’s move on to a rule of thumb to predict the effect of a single permanent change in diet or exercise for the average overweight person.

Simplified Model for the Average Person

I’m frequently asked how long it will take to become lean or lose a certain amount of weight. I usually say that’s the wrong question; that it’s best to take weight loss one week at a time. Rushing the process is the most common mistake people make; it usually torpedoes their weight loss plans. Perhaps it’s time to change my stock answer. The Hall team has offered a simple formula that allows average overweight people to realistically evaluate their weight loss goals.

After a long and complicated recital of the underlying research data—which I’ll spare you—Hall and colleagues set out the formula in one long but straightforward sentence.

“Every permanent change in energy intake of 10 calories per day will lead to an eventual weight change of about one pound, and it will take about one year to achieve half of the total weight change and 95% of the total weight change will result in about 3 years.” That sounds familiar because we just talking about a similar weight loss trajectory above.

“[Our model] is a good reality check for how long weight loss takes, and what changes in eating and exercise are required to achieve and maintain goal weigh,” Dr. Hall told Science Daily (August 26, 2011).


Here’s how I suggest putting the rule-of-thumb into action.

*  *  *

The formula is for the average overweight person with a body mass index (a measure of a person’s weight in relation to his or her height) between 25 and 30. A quick Google search will explain how to calculate BMI. Frankly, I wouldn’t worry about it. All you have to do is look in the mirror to decide whether you need to lose weight, and take a pretty good guess how much you need to lose. No matter where you stand on the BMI scale, you’ll find the simplified model to be a godsend.

Here’s an example of how it works.

If your goal is to lose 50 pounds, the formula says you will need to create a steady daily energy deficit of 500 calories (10 x 50). The best way to do that is to reduce calorie intake by 250 and increase physical activity by a like amount. That way your fat cells will notice the difference, but you probably won’t. (Avoid the temptation to cut more severely.)

Do that consistently and you’ll lose about 25 pounds the first year and the second 25 pounds over the next two years. You’ll lose the full 50 pounds in about 3 years. (It took you longer than that to put the weight on, and you should expect to take a while losing it.) That would be a terrific result, accomplished with little, if any, discomfort. What’s more, you won’t be tempted to regain the weight. Continue eating sensibly and exercising regularly and you’ll be lean for life.

Some people will lose faster and others slower, but almost everyone should be successful on this plan. If you’re eating the typical American diet of mostly processed foods with lots of sugar and salt added, a switch to a balanced diet of whole or minimally processed foods will put on track to meet your goal. You won’t even have to count calories. Add two days a week of aerobic exercise and two days of resistance training, and stay active in between workouts and you’ll be amazed at how much better you’ll look and feel.

What’s holding you back? Get started today.

For more details, see our Diet and Training Philosophy in Brief: http://www.cbass.com/PHILOSOP.HTM

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