Welcome to the book review section of NutritionWonk, where we try to deconstruct popular diets by examining the science underlying the major claims.
Introduction: Always Hungry and the Diet Book Literary Tradition
Always Hungry, by Harvard endocrinologist Dr. David Ludwig, is the latest bestseller claiming to buck the conventional wisdom. Although plenty of diet books are written by MD’s, Dr. Ludwig is not a fad diet doctor.
Dr. Ludwig has built a career of research and practice in weight management, having published over a hundred studies, including many on the effects of glycemic index. Additionally, he is the director of the New Balance Foundation Obesity Center and the founding director of the Optimal Weight for Life (OWL) program at Boston Children’s Hospital. In summary, Dr. Ludwig is not one of the many diet book authors who expects his MD to convey clout; he has significant scientific and medical experience working in obesity prevention and weight loss.
The primary aim of Always Hungry is to provide a diet that allows followers to lose weight at a steady pace without feeling hungry. Dr. Ludwig designs the diet using a combination of lower glycemic index (GI) carbohydrates, healthy fats, and moderate protein. The book provides a complex protocol of exacting menu plans and tracking sheets, which seem daunting, but may ensure that people who attempt the diet are fully committed.
The book comes standard with all the features of a best-selling diet book:
The enthusiastic oversell at the beginning
Anecdotal reports that claim the diet not only reduced weight, but solved life problems unrelated to weight for participants
A science context section heavy on the persuasive writing and light on the literature review
A diet much more complex than the previous half of the book claimed it would be
These are four major components of every bestselling diet book, Always Hungry, included. It fits into its milieu the same way a teenage girl with two love interests fits into the YA genre. It’s a fact of life.
But, in each of these categories Always Hungry rises above the rest: It features success stories with real people from the Always Hungry pilot program; it contains actual science; and the diet, while complex, seems delicious and healthy.
There were plenty of claims in this book that could be examined for scientific context, but I picked the major one to unpack.
Major Claim: Glycemic index and processed carb content determines the amount a person will eat, whether they will store fat, and how soon they will be hungry.
Therefore, by lowering the glycemic load of your diet by slightly increasing fat and choosing unrefined carbs, weight will come off.
What are glycemic index and glycemic load?
Glycemic index (GI) is a measure of how much a specific food item will raise blood sugar after consumption. In turn, that blood sugar will stimulate a proportional amount of insulin release, shunting glucose into body tissues and bringing blood sugar back down. Foods with a high glycemic index cause greater spikes in blood sugar. All foods are compared to the glycemic index of glucose, which is assigned a value of 100.
Glycemic load (GL) is the glycemic index times carbohydrate content. In theory, a mixed meal can have a low glycemic index, due to a high fat content, for instance, and still have a high glycemic load because it is also high in carbohydrate. In this way, glycemic load can be confounded with energy density in some scenarios.
The defense of GI and GL in the book functions more like a persuasive essay than a thorough review of the literature. While Dr. Ludwig’s extensive work has shown positive outcomes using a glycemic model for designing weight loss diets, the totality of the literature is mixed.
This is largely because observational studies, studies that follow people over time and ask them to recall their food intake, show benefits of lower GI and GL diets, but trials, multi-armed experiments, can fail to show a difference.
The most notorious of these, perhaps, is the OmniCarb randomized, crossover trial. In this experiment, healthy adults ate four different diets for 5 weeks each with a 2-week washout period. The diets were high carb, high GI; high carb, low GI; low carb, high GI; low carb, low GI, and all meals were provided. At the end of the trial, no benefits were found for low GI diets compared to high GI.
In a study published last year in Cell, a group of scientists in Israel determined that post-meal glucose levels varied widely between individuals, suggesting that a food’s GI might not be the same for you as it is for someone else.
Now, as Dr. Ludwig has pointed out, clinical nutrition trials are not without flaws. Feeding studies enlist highly motivated individuals and provide calorie-controlled meals. The satiating effect of a low GL diet that promotes lower intake won’t make a difference– all participants are eating the same amount. Further, plenty of clinical nutrition trials can have null results, but dietary advice doesn’t change because it is based on consistent statistical trends in observational data.
So why does this low GL, higher fat diet work? A low glycemic load likely does decrease appetite compared to eating simple carbohydrates: a cheese sandwich with whole wheat bread is going to be more filling than three dry pieces of toast.
There are several reasons for this:
Inclusion of protein and fat in a meal increase satiety.
A meal of unprocessed foods may be digested more slowly in the gut, triggering the “ileal brake,” which slows intestinal motility and influences satiety.
It allows for a steadier release of blood glucose after digestion and prevents large spikes in insulin that can lead to increased hunger after glucose levels fall.
These effects are covered in Always Hungry and are well-supported, though they may vary slightly from person to person. So sure, if you follow a low GL diet without fail, you can lose weight and feel less hungry.
The book tries hard to convince us that the main reason we overeat is because of post-meal insulin surges. Strangely, the reasoning that insulin starves body tissues while feeding only fat cells is laced throughout the book and promotional materials, and is largely derived from citations of Gary Taubes’ books and articles, which is somewhat problematic. The only explanation I could think of for such an oversimplification is to make the low-GI concept easier to follow, even if it isn’t quite right.
The scientific-context section of the book pays little attention to other potential reasons for overeating, like:
After the scientific justification, Dr. Ludwig launches into the “how to” of the diet. This part is complicated; it starts with a two-week plan followers are supposed to adhere to for every meal. Weekly prep days involve creating a number of sauces and salad dressings, even roasting several ounces of nuts each week, which are then doled out later in small servings.
The Always Hungry site has numerous charts and trackers dieters are meant to print and fill out as they follow the diet. These include daily trackers that ask you to estimate the level of processed carbohydrates you have eaten each day.
Though the diet is healthy and probably will keep a dieter sated, it lacks the simplicity of an Atkins style (no carbs) or Weight Watchers (count calories) diet. But only diet books say dieting is easy.
In conclusion, Always Hungry contains a healthy diet based on solid science. While the writing fully embraces the cheesy language and optimism of its genre, it surpasses fad diets in many respects.