You Know Obesity, Right? Fat Chance!
Did you know the "fact" that 3,500 kilocalories of dietary excess or deficit will result in 1 pound of weight gain or loss is wrong? That's right, this holy grail of weight loss is based predominantly on short-term experiments in men on very low-energy diets (<800 kcal). So, maybe the patient who insists they gained weight from eating a couple slices of pizza isn't delusional after all.
This is just one of the myths exploded by Krista Casazza, PhD, RD, an assistant professor in the department of nutrition sciences at the University of Alabama in Birmingham, and a multidisciplinary group of colleagues in a New England Journal of Medicine article1 enticingly entitled "Myths, Presumptions, and Facts about Obesity."
The researchers reviewed many commonly held beliefs about diet and obesity, assessing the level of evidence supporting each. They categorized these beliefs as myths (those "held to be true despite substantial refuting evidence"), presumptions ("beliefs held to be true for which convincing evidence does not yet confirm or disprove their truth"), and facts ("propositions backed by sufficient evidence to consider them empirically proved for practical purposes").
The authors debunk the 3,500-kcal rule in relation to the oft-repeated assertion that small sustained changes in energy intake or expenditure will produce large, long-term weight changes. Or, as national health guidelines and reputable websites advertise, that someone who walks an extra mile every day will lose more than 50 pounds over a period of 5 years, assuming no compensatory increase in caloric intake. "There has been a lot of modeling and it's been demonstrated time and time again that the evidence is just not there to support it," said Dr. Casazza. In fact, the amount of expected weight loss in the above scenario is more like 10 pounds.
"Any change in mass will alter the energy requirements of the body," said Dr. Casazza. "When you lose a pound, you don't lose exactly a pound of fat necessarily. Rather, you probably lose some lean tissue, too, and the metabolic expense of maintaining fat and lean tissue differs. There will be other concomitant changes, too, such as in hormones, so it's much more complex than just a pound of fat, which is what is often reported."
To refine the 3,500-kcal rule, a huge amount of data would need to be collected in both men and women, across age ranges and with different body habitus. Individual variability would probably be substantial, noted Dr. Casazza.
Most Important Meal? Nah
The first presumption challenged by the article is the value of breakfast. While commonly repeated wisdom says that the regular consumption of breakfast is protective against obesity, in fact two randomized clinical trials specifically studied the outcome of eating versus skipping breakfast showed no effect on weight in the total sample.
"If you skip breakfast, you tend to eat more in the afternoon than you would normally eat had you had breakfast, of course, because you're hungrier," said Dr. Casazza. "But if you are still at an overall calorie deficit for the day, then you're not going to gain weight, according to the evidence we have.
"Now whether or not that translates into a presumption that it's fine to skip breakfast is a different question. There is some speculation that skipping meals causes you to store more fat because you can't metabolize all the calories," added Dr. Casazza. "We haven't presented that; we're just dealing with the value of breakfast issue."
She added that, as a practicing dietitian, she would not press someone to eat breakfast if they really didn't want to. "I've always gone by the presumption that it's better metabolically speaking and for purposes of weight loss to eat multiple, small meals throughout the day, but forcing someone to eat if they really don't want to, I don't really see the value in that."
Fact: Exercise Improves Health. Period.
"For cardiologists, I think that fact #3 on our list—'regardless of body weight or weight loss, an increased level of exercise increases health'—is probably the most important fact in terms of clinical care," said Dr. Casazza, adding that increased exercise should almost always be included as part of the first-line prevention for chronic disease. "It's a way of mitigating the health-damaging effects of obesity on the heart, liver, kidneys, and pancreas. So, even if they aren't successful in losing weight, when a sedentary person starts to exercise, they increase lean mass, and that's beneficial."
Many of the misconceptions about dieting and obesity revolve around a failure to understand the many facets of energy balance. It's often just reported as "energy in and energy out," but there are a lot of other factors that come into play, according to Dr. Casazza. There are partitioning issues, genetic influences, different metabolic processes, hormones, the thermic effects of food, resting expenditure, and active expenditure. She said, "These all change depending on the person, their stage of life, whether they are growing or not growing, whether they have chronic disease or not."
Although obesity is an urgent public health issue, "scientific principles remain unchanged," the authors wrote. One important question to consider when determining whether any particular dogma is really true: "How could someone actually know that?"
Indeed, this question is probably never seriously considered regarding another oft-stated myth that an episode of sexual activity burns between 100 and 300 kcal (per participant). Reality: To test this would require one participant wearing a mask in order to do indirect calorimetry and a third party would have to be on hand to start and stop the activity and measure heart rate. "I mean, theoretically, you could do it, but it wouldn't be an easy study to conduct," said Dr. Casazza. "And again, you couldn't just generalize the results from a small study of 20-year-old males. You would have to also study women, older and younger individuals, different body habitus, etc."
Roger Blumenthal, MD, director of Johns Hopkins Ciccarone Preventive Cardiology Center, told CardioSource WorldNews, "I agree that this is a provocative article and the amount of top quality dietary research is lacking. [The article] shows that we need to fund better quality, longer-time lifestyle intervention trials."
Clearly, he added, better dietary and exercise habits are the cornerstone of preventive cardiology. "I tell my patients what [Dr. Neil Stone] taught me when I first joined the Hopkins faculty: 'Eat less, eat smarter, and move around a lot more!'"
1. Casazza K, Fontaine KR, Astrup A, et al. N Engl J Med. 2013;368:446-54.
< Back to Listings