As if Mondays aren't bad enough, I found out today courtesy of my Wall Street Journal RSS feed that perhaps researchers have been mistaken in their calculations of calorie consumption and weight loss. So all of the little steps I was taking really don't add up to the ultimate diet equation?

Well, sort of. The problem is that the formula used for "diet math" - 3,500 calories equals one pound - isn't really all that simple.¹ This rule of thumb works well in the short term, WSJ says, and with small shifts in weight, but the rule breaks down over long periods, because as a person's weight changes, so does the body's energy needs.

WSJ reporter Carl Bialik uses a simple cookie ... mmm, cookie ... where was I? Oh yes.

Consider the chocolate-chip-cookie fan who adds one 60-calorie cookie to his daily diet. By the old math, that cookie would add up to six pounds in a year, 60 pounds in a decade and hundreds of pounds in a lifetime.

[For the non-mathematically inclined, 60 calories/day x 365 days/year = 21,900 calories/year divided by 3,500 calories/pound = 6.25 pounds/year.]

However, this assumes we gain or lose weight in a vacuum, with a simple energy in/out exchange not impacted by any other physiologic processes. And that's where the cookie crumbles, researchers say.

First, how we got to the 3,500 rule in the first place - fat has about 4,500 calories per pound, and protein has about 2,000. So, a pound of body mass which is on average 25% lean tissue (protein/water-rich muscle) and 75% fatty tissue has about 3,500 calories of energy.

In the short term, this rule works generally as you'd expect, as your body is still operating on its original system. Say you normally eat a 2,000 calories/day diet and you weight 150 pounds (67.5 kg, for the metric folks). If you want to lose weight, you reduce your caloric intake. So, according to the old formula, if you want to lose one pound/0.453 kg (3,500 cal) in a week, you eat 500 calories less per day, so you'd eat 1,500 calories per day and hey presto, you fit into your skinny jeans again.

In the long term, though, your body isn't operating on its original system. You lose weight that first week (or first few weeks) because your body still thinks you weigh 150 pounds and as such you still need your 2,000 calories per day. But eventually, like any good self-regulating system, your body will adapt to its new environment. Once you lose enough weight - I don't know, maybe 15 pounds - your body will adjust to the new needs of your 135 pound body. You need less energy to sustain your bodily processes than you did at 150 pounds. Suddenly, that 1,500 calories is just right for your body needs, and instead of losing weight you level off and stay stable. This is why weight loss always starts off so well, and then it gets harder to keep shedding pounds.



Annoying if you're trying to lose/gain weight? Yes. If you're trying to lose weight, you're going to have to work harder as time goes on. Same if you're trying to gain weight. For the individual, this could be no big deal, an inconvenience, or a huge barrier.² But if you look at this from a national public health point of view, the idea of small steps could need a major overhaul.

Think about health campaigns you've seen that encourage you to do the little things - walk up the stairs instead of taking the elevator, or replace one can of soda a day with water, etc. Little changes will lead to big changes and a healthier lifestyle, says the mantra. But the new math says these little steps will barely make a dent, WSJ says.

I want to emphasize that just because little steps won't have quite the impact we had hoped, it doesn't mean they aren't still important. They are, and could lead to bigger and better things.

"As clinicians, we celebrate small changes because they often lead to big changes," said Dr. David Ludwig, director of the Optimal Weight for Life program at Children’s Hospital Boston and a co-author of the JAMA commentary. "An obese adolescent who cuts back TV viewing from six to five hours each day may then go on to decrease viewing much more. However, it would be entirely unrealistic to think that these changes alone would produce substantial weight loss."

We need to be realistic, Ludwig says. That doesn't mean throwing up your hands and quitting, but just realizing how your body works and adjusting for that.

This is not to say that the push for small daily changes in eating and exercise is misguided. James O. Hill, director of the Center for Human Nutrition at the University of Colorado Denver, says that while weight loss requires significant lifestyle changes, taking away extra calories through small steps can help slow and prevent weight gain. "Once you’re trying for weight loss, you're out of the small-change realm," he said. "But the small-steps approach can stop weight gain." While small steps are unlikely to solve the nation's obesity crisis, doctors say losing a little weight, eating more heart-healthy foods and increasing exercise can make a meaningful difference in overall health and risks for heart disease and diabetes.

Ludwig says that if we stick with the original caloric formula, we're kidding ourselves about the outcomes. "We need to know what we're up against in terms of the basic biological challenges, and then design a campaign that will truly address the problem in its full magnitude. If we just expect that inner-city child to exercise self-control and walk a little bit more, then I think we're in for a big disappointment."

A revised diet equation also helps us understand why men, the stupid jerks, lose weight like it's the easiest thing in the world while women struggle. Losing a pound of more fatty body tissue requires a larger energy deficit (read: fewer calories, or more exercise) than is required to lose the same amount of leaner body tissue. Because women tend to have more body fat than men of similar weight, it takes more for us to lose weight than a guy. Again, jerks. It also helps us understand how you can gain weight back so quickly - if you lose weight and need less calories, going back to your regular diet/exercise routine will overwhelm your less-needy body and you gain weight quickly.

The solution, say JAMA authors Ludwig and Katan, is not so much on the individual but on the whole infrastructure in which we live.

These calculations suggest that small changes in lifestyle would have a minor effect on obesity prevention. Walking an extra mile a day expends, roughly, an additional 60 kcal compared with resting—equal to the energy in a small cookie. Physiological considerations suggest that the apparent energy imbalance for much of the US population is 5- to 10-fold greater, far beyond the ability of most individuals to address on a personal level. Rather, an effective public health approach to obesity prevention will require fundamental changes in the food supply and the social infrastructure. Changes of this nature depend on more stringent regulation of the food industry, agricultural policy informed by public health, and investments by government in the social environment to promote physical activity.

Well that ought to be an easy fix, no?

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Hall, KD. Int J Obes (Lond). 2008 March; 32(3):573–576.
Hall, KD. IEEE Eng Med Biol Mag. 2010 Jan-Feb;29(1):36-41.
Katan MB, Ludwig DS. JAMA. 2010;303(1):65-66.

¹ The term "calorie" is used throughout as that is the general term used in discourse, but just to to be scientifically accurate, all of these values actually represent "kilocalories."
² I now feel better about my splurge this weekend. Since I moving back across the country this week, I took the opportunity to imbibe one last time in heavenly sour cream-glazed Timbits. I felt guilty at the time but justified it by thinking that soon there will be several states between Timbits and me, so I won't have the temptation or opportunity to indulge in the foreseeable future. While it's not as healthy as an apple, at least I won't gain 800 pounds just by eating a few Timbits. Or, if I do, eventually my weight will level off. So there's hope.