Apr 12 2012
There is an ongoing debate about the best strategies for long term weight control. I have repeatedly taken the position that, based mostly upon the clinical evidence but also what makes sense, that weight control is a matter of calories in vs calories out. The evidence consistently shows that exercise (increasing calories out) is extremely valuable to overall health but also specifically to weight control. Calories in is the tricky part.
There is no question that reducing caloric intake is critical to weight control, and that all diets that result in weight loss have one thing in common – reduced calories. It is difficult to achieve sustained calorie control, however. There is the pesky problem of hunger. Our bodies are very effective at regulating our eating behavior, and generally oppose underconsuming calories to result in weight loss. It is very difficulty to consistently resist such basic urges as eating when hungry.
This difficulty is exactly why there are so many fad diets, diet products, and beliefs about how to lose weight. No strategy works well, and I don’t have the magic answer, but we can look at the data we do have to see which strategies work better than the others. Recently a new study did just that, reviewing data from the 2001–2006 National Health and Nutrition Examination Survey (NHANES). This is a retrospective study based upon voluntary reporting, and therefore there are many possible sources of bias. The strength is that it is a fairly large study, looking at 4021 obese adults, and the result are reasonably representative of the general population in the US.
The study found that 40% of those in the study reported losing >5% of their body weight in the last year through deliberate dieting, while 20% lost >10% of their weight. These numbers are higher than we would suspect from previous evidence. They may represent a bias toward overreporting success, but they may also indicate that perhaps weight loss success is higher than previously suspected, at least in the short term. Unfortunately, most people who do lose weight will gain it back.
The more interesting results are the correlations between weight loss strategy and weight loss success in the data. The researchers found a correlation between reporting successful weight loss over the previous year and reducing fat in the diet, increased exercise, joining a weight loss program, and prescription diet medication. They found no correlation between success and using a diet plan, over-the-counter diet pills, liquid diets, or eating diet products.
These are interesting results, with the caveat that this is just one study with the weaknesses I discuss above. The results are, however, in line with other clinical research on weight loss. Reviews generally conclude that reducing total fat in the diet is an effective strategy for weight loss. This is probably because fat is more caloric (9 calories per gram) than protein or carbohydrates (4 calories per gram), so reducing fat is a good way to reduce total calories. Still – total calories are what count.
The justification for many fad diets is the manipulation of macronutrient percentages to achieve either reduced hunger (and therefore reduced calories) or improved metabolism (and therefore increased calorie burning). Some fad diet books like The Zone Diet confuse the metabolism argument, saying that being in the “zone” of macronutrient balance achieves greater efficiency. But efficiency, getting more out of the food you eat, would work against weight loss. Energy inefficiency would result in weight loss. That confusion aside, the metabolic argument has not stood up to research specifically looking at calorie burning. There does not appear to be any metabolic advantage to either low carb or high protein diets.
What about the hunger argument. The evidence does show that high protein, low carb diets (and probably it’s the protein and not the carbohydrates) do reduce hunger over the short term (3-6 months), but this advantage appears to be very modest and goes away after 6 months. So high protein/low carb does not appear to be an effective strategy for long term weight loss, and after more than a decade of research and many study designs no one has demonstrated a long term benefit to these diets.
It is no surprise that diet supplements don’t work. They are poorly regulated and often are just a random assortment of vitamins and herbs without any scientific justification to suspect that they would be effective. Many diet aids include caffeine or a similar stimulant to make the user feel as if they have more energy, but stimulants are not effective long term for weight loss as your body quickly adjusts to them.
Weight loss programs do appear to be effective, probably because they make it easier for dieters to estimate their caloric intake and they often include a social support network, which itself seems to predict dieting success.
I occasionally review the literature on the question of weight control, especially when new interesting studies are published. After many studies looking at this issue from many angles the results boil down to a few simple rules. For weight control exercise on a regular basis and find some way to control overall caloric intake long term. There are no magic diets, special foods, or optimal proportions of macronutrients that will make calorie restriction easy. Reducing total fat seems to be helpful. It is also helpful to include more vegetables in the diet, because these tend to be lower calorie (and are good to have in your diet in any case). Having emotional support and using aids to help in calorie estimation are also helpful. Just recording what you eat every day helps.
Whatever you do, focus on the long term. Short term strategies are doomed to fail long term, and are counterproductive.
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