Obesity is very difficult to impossible to treat. The most common prescription, and indeed the prevailing conventional wisdom, is that “lifestyle” changes are the best solution. This typically means diet and exercise. However, this has been extensively studied. Across the population, diet and exercise, each individually and in tandem, are completely useless to treat obesity, in the long term.
In the case of exercise, randomized controlled trials (RCTs) don’t even show a short-term benefit. One 2007 meta analysis by Franz et al looked at the results of all sorts of different interventions. For exercise-alone prescriptions, it found that the treatment groups lost no weight at 6 months (well, less than 2 kgs, but even this number comes only when you look at those who remained in the study). Indeed, after a year, the control groups actually lost more weight than the treatment groups. The total weight change was small and close to zero throughout.
In the case of diets, particularly the most common low-fat and low-calorie diets, a very large meta-analysis of RCTs with a combined N > 60,000 (of which ~48,000 came from a single mammoth trial) and a study duration of 2.5 – 10 years, found that diet was completely ineffective for weight loss. The subjects showed no aggregate permanent weight loss at the end of the study period. The largest of these studies, the one by Howard et al (2006) found little change, a total loss (over 3 years) of less than 1 kg (and a difference between control and treatment groups of 1.29 kg, favoring treatment).
As for diet and exercise combined, several studies in both previous meta-analyses look at trials which tested both together. The result was the same: little to no significant aggregate weight loss, especially after longer periods of time.
This is true of low-carbohydrate diets as well. One meta-analysis looked at RCTs. Each of the trials were individually small (n = 11 – 153), but all told there were 712 subjects in the low-carb trials. The duration of studies ranged from 12 to 24 months. The total average weight lost with the low-carb diet groups was on the order of 4 kg! And that’s with considerable attrition in the studies. Low-carb diets don’t work much better, either.
A new randomized comparison trial (Bazzano et al, 2014) of a low-carb vs a low-fat diet (N = 148) found only a weight loss of 5.3 kg after 1 year with the low-carb diet, but only 1.2% change in body fat percentage.
The question is how much I am harming myself by being obese? Should I just sit and wait till a heart attack or signs of diabetes hit me?