Case study: Dr. David Ludwig's Always Hungry
Recently, a book called Always Hungry?: Conquer Cravings, Retrain Your Fat Cells, and Lose Weight Permanently landed on my desk. Like dozens of books I've seen before, it makes big promises.
But this book wasn't authored by a woo-loving celebrity like Paltrow. The book came from Dr. David Ludwig, an esteemed endocrinologist and researcher affiliated with Harvard Medical School who has run dozens of clinical trials and seen thousands of patients in the 20 years he's practiced medicine.
Unlike many other diet book authors, Ludwig offers a strong scientific theory for his diet: a model of obesity he's developed based on his and others' research. The "carbohydrate-insulin hypothesis," which journalist Gary Taubes and others have also extensively promoted, contends that a diet heavy in carbohydrates (especially refined grains and sugars) can lead to obesity because they increase insulin in the body, and cause the body to hold on to fat.
The classic approach to dieting — in which calories in general are restricted — fails, Ludwig argues, because it doesn't account for the effects calorie restriction and refined carbohydrates have on the body. As an alternative, Ludwig says dieters should forget about calories and focus on reducing carbohydrates and increasing fat intake to feel more satiated and lose more fat in the long run. His discussion of the science here is lucid and interesting.
But what readers may miss in the way this theory is presented in the book is that it's still very much a work in progress, and the subject of heated debate among obesity scientists. Not everyone agrees that this approach to weight loss is superior, and there's high-quality evidence that contradicts it.
The real problem with diet books is what comes next: the diet itself. Publishers are not interested in a book simply running through some interesting, if preliminary, theory on how to eat. They want a very specific plan. They want bold promises about results. And these plans, though sometimes based on promising science, are not rigorously tested among dieters. Worse, in proposing a singular plan, they suggest there is One Right Way for people to eat, which isn't the case. The best diet, in truth, is the one you, personally, can stick to.
In this case, the closest thing Ludwig has to a test of his diet is a pilot study that followed 237 people, the results of which he references heavily throughout the book. "Most people in the pilot initially lost 1 to 2 pounds a week, a few lost even more, some a bit less," he writes. "In addition to weight loss, participants consistently reported other benefits that predict long-term success, including: decreased hunger; longer-lasting satiety after eating; great satisfaction with food."
In a subsequent email, Ludwig said, "The pilot test was never intended as proof. The higher-fat diet I recommend is based on dozens of studies from my research team and hundreds of studies by others. No diet ever recommended, including by the government, has been proven by a definitive randomized controlled trial. Consider, for example, American Heart Association No-Fad Diet: A Personal Plan for Healthy Weight Loss. That title doesn't make clear that not everyone will lose weight or that the weight loss might be temporary. Further, no long-term trial proved that calorie restriction, the recommended approach, was healthy."
Indeed, the book clearly states that the pilot is not scientific and was instead designed to generate feedback on the diet. And yet, Ludwig heavily draws on the weight loss "success stories" from pilot participants throughout the book to make very specific claims about the transformation his diet can confer to anyone who tries it: "I'm confident that Always Hungry? will help you achieve lasting weight loss, experience increased vitality, and enjoy a healthy life," he writes.
I asked Ludwig why he published the book before he had tested the diet with a higher quality, longer-term study. Ludwig's pilot study ran for only 16 weeks, and as every obesity researcher knows, many people following a new diet lose weight initially; the big question is what happens afterward. The data we have on this is sobering. Only a tiny percentage of people who try to lose weight on a diet succeed, and many more actually gain weight in the dieting process.
"Science is always evolving," Ludwig told me. "But in public health you can't wait for the final answer before deciding how to proceed."
In an email, he added, "The relevant question isn't whether there's proof, but rather how the evidence for alternative approaches compares to conventional recommendations. For 40 years, the public has been told that the best way to lose weight is to cut back on calories and fat. But this advice has failed miserably in practice. Is it fair to demand that new approaches be subject to far higher standards of evidence than has ever applied to existing recommendations?"
A recent review of the research on different types of diets in the Lancet (by Ludwig and others) finds low-carb diets outperform low-fat diets. But as a related commentary points out, the difference in weight loss among groups of dieters is tiny: "Participants prescribed low-carbohydrate diets lost only about 1 kg of additional weight after 1 year compared with those advised to consume low-fat diets."
Dr. Oz The Bulletproof Diet
Update, April 27: