Weight-loss diet books continue to occupy the top of the bestseller lists. However, over the past decade there has been a shift in the way these diets are framed, and in the types of scientific claims underpinning the diets.
A key feature of many popular weight-loss diets since the 1970s has been the claim that the macronutrient ratio—proportion of fat, carbs and protein—is the major determinant of whether a food or dietary pattern promotes weight gain or weight loss. Low-fat, low-carb, high-fat, high-protein—some combination of some of these macronutrient prescriptions—have dominated the weight-loss scene in the late twentieth century.
In recent years, weight-loss diet books have continued to make reference to the ideal macronutrient profile for weight loss, but with a greater focus on the particular foods to consume or avoid: meat, wheat, grains or sugar. However, these diet books also place greater emphasis on how nutrients and foods affect specific bodily processes and functions related to weight gain and loss. Their focus has shifted down to the cellular and molecular level of our bodies, and onto hormones such as insulin, the control of blood sugar levels, the regulation of fat storage in cells, and brain-satiety signals. Diet book authors now offer precise and definitive scientific explanations of the multiple pathways through which nutrients, foods and dietary patterns affect our metabolism and mediate fat storage, hunger cravings and energy levels.
The focus on nutrients, and claims about the precise role of nutrients and foods on bodily health, are features of what I refer to as the ideology of nutritionism. Some of the characteristics of nutritionism are the reductive, simplified and exaggerated claims that are often asserted about the role of nutrients on bodily health. The idea that fat is ‘bad’ is an example of such a simplified and decontextualized nutritional knowledge, but that claim dominated dietary advice for decades.
There have also been significant changes in the way nutrients, foods and the body are understood across three distinct eras of nutrition science and dietary advice. And these changes are reflected in the way weight-loss diets have been framed and promoted over the past century.
From calorie counting to the fear of bad nutrients
In the early twentieth century—during the first era of "quantifying nutritionism"—calorie counting first emerged as a weight management strategy. The energy balance equation—calories-in, calories out—reflected a view of food as if it were made up of uniform calories, and a view of the body as a calorie-counting machine. This energy balance equation requires no understanding of internal bodily processes, nor of the nature or nutritional composition of the foods being consumed beyond their estimated calorie values. Despite a century of advances in nutrition science, the idea that "a calorie is a calorie"—regardless of the food source of the calories—has again become the official weight management message over the past decade, particularly since the decline of the low-fat campaign.
The period of the 1960s to the 1990s corresponds to the era of "good-and-bad nutritionism," in which the notion that there are clearly distinguishable "good" and "bad" nutrients first emerged. Negative dietary messages dominated the nutriscape in this era, with the focus on the bad nutrients and foods to avoid—such as fat and cholesterol—and on risks associated with consuming them. The assumption underpinning mainstream dietary guidelines and weight-loss advice in this period was that the macronutrient ratio is a primary driver of weight changes, regardless of the types of foods in which these macronutrients are consumed.
The fear of dietary fat, in particular, suffused mainstream dietary advice for weight management, primarily because it contained twice as many calories per gram than carbohydrates and protein. Yet fat was also portrayed as the most fattening of macronutrients—and more readily converted into body fat—even on a calorie-for-calorie basis. For example, in his best-selling 1993 weight-loss diet book "Eat More, Weigh Less," Dr. Dean Ornish argued that “eating fat makes you fat, even if you take in fewer calories.”
Running alongside and challenging the low-fat orthodoxy was Dr. Atkins' low-carb diet, which turned mainstream dietary advice on its head by characterizing carbs as the primary—if not the only—fattening macronutrient, particularly due to their contributions to raising blood sugar and insulin levels. Here we see Dr. Atkins and the low-carb movement already beginning to popularize the language of hormones and turning our attention to inner bodily processes. Despite their disdain for carbs, it is the so-called refined carbs—refined grains and sugars—that low-carb proponents primarily blame for obesity and poor health.
High-protein diet plans—such as Michael and Mary Eades’ Protein Power—have also been a feature of diets since the 1990s, though these are also often relatively low in carbs. High-protein diets tend to emphasize the claimed satiety value of protein. French doctor Pierre Dukan, creator of the high-protein/low-carb Dukan Diet, claims that protein is the macronutrient that the body has to work hardest to digest, as well as being the most satisfying. Many paleo diets are also framed as high-protein diets.
From macronutrients to hormones and internal bodily functions
Since the mid 1990s there has been a further shift in the nutritional zeitgeist to a new era of "functional nutritionism." While the vilification of bad nutrients persists, there has also been a new emphasis on a new range of beneficial or "functional" nutrients—such as omega-3 fats, vitamin D, probiotic bacteria, antioxidants, resistant starch—and the way these nutrients target and optimize specific internal bodily processes and functions. In a move away from the earlier focus on single nutrients, the types of foods promoted are “nutrient dense” foods—foods that contain a concentrated dose of a range of these good/functional nutrients, while minimizing any so-called bad nutrients.
In this functional era, there are also more explicit references to these inner body processes within nutrition education and food marketing. For example, advertisements make reference to the way yoghurt introduces "good bacteria" into our stomachs, or the way cholesterol-lowering margarines block the absorption of cholesterol into the blood. So-called "functional foods"—foods that are high in these "functional" nutrients—use these sorts of images and claims in their advertisements and on the labels. We are thereby encouraged to think about and experience our own bodies in these functional terms.
The latest wave of weight-loss diet books and programs embrace these new ways of imagining and engaging with food and the body. Many of these weight-loss diets continue to blame one specific nutrient, food component or food group for weight gain. But their authors also claim to have precise knowledge of the specific and multiple pathways through which these food components affect the body. This includes claims regarding the way foods and nutrients directly influence the way cells store fat, or control blood sugar levels and satiety. A common feature of some of these diets is their focus on the hormones that regulate these bodily processes, such as insulin or leptin.
The anti-wheat polemic of William Davis’ best-selling "Wheat Belly" puts forward definitive claims regarding the way modern varieties of wheat affect a range of bodily functions, in large part due to its high gluten content. Wheat, Davis tells us, can “reach deep down into virtually every organ of the body, from the intestines, liver, heart, and thyroid gland all the way up to the brain. In fact, there’s hardly an organ that is not affected by wheat in some potentially damaging way.” With little understatement, he also claims that wheat—including whole wheat—is uniquely fat inducing, particularly due to its contribution to blood sugar fluctuations and insulin spikes: “I’d go as far as saying that overly enthusiastic wheat consumption is the main cause of the obesity and diabetes crisis in the United States.”
Yet the book also acknowledges that it is refined wheat flour that is mostly consumed—and the sorts of foods in which this refined flour is found—that are the major problems with contemporary eating habits. Despite Davis’ focus on wheat, this is essentially a low-carb, calorie-restricted and anti-processed food diet.
Low GI (Glycemic Index) diets are based on the claim that the extent to which particular foods raise blood glucose levels, and by extension insulin, can be precisely calculated. Like many low-carb diets, low-GI approaches focus attention on insulin and blood sugar as the primary fat storage determinants. However, GI advocates don’t encourage people to eat fewer carbs, but instead to seek out "smart carbs" that supposedly raise blood sugar slowly, and that they claim thereby help control hunger cravings.
Haylie Pomroy’s Fast Metabolism Diet claims to target your body’s thyroid hormones in order to “reprogram” your metabolism into fat-burning mode. This precise eating strategy involves a “systematic rotation of targeted foods on specific days at strategic times” in order to enhance the particular types of thyroid hormones that promote fat burning rather than fat storage. This includes switching from a high-carb/moderate-protein diet to low-carb/high-protein foods in the first two phases of the program. But by eliminating wheat, corn, dairy, soy, sugar, artificial ingredients and alcohol, many highly processed foods and sweets are also effectively eliminated, while also advocating very low calorie meals.
Other diet books tapping into the hormone theme include Michael Aziz’s "The Perfect 10 Diet: 10 Key Hormones That Hold the Secret to Losing Weight and Feeling Great-Fast!"; Natasha Turner’s "The Hormone Diet: A 3-Step Program to Help You Lose Weight, Gain Strength, and Live Younger Longer"; Jillian Michael and Mariska Van Aalst’s "Master Your Metabolism: The 3 Diet Secrets to Naturally Balancing Your Hormones for a Hot and Healthy Body!"; and Leo Galland’s "The Fat Resistance Diet: Unlock the Secret of the Hormone Leptin to Eliminate Cravings, Supercharge Your Metabolism, Fight Inflammation, Lose Weight & Reprogram Your Body to Stay Thin."
Michael Mosley and Mimi Spencer’s best-selling "Fast Diet," or 5:2 diet—5 days of normal eating, 2 days of fasting—presents precious little evidence in support of this diet beyond the odd mouse study, a few personal anecdotes and the claim that “your body is designed to fast.” Drastic calorie restriction (i.e., eating less) is hardly new. But starving oneself for just two days a week has proven a novel enough eating strategy to capture the public imagination in 2013, compared with the alternative of just eating a bit less—and eating better quality food—all week long.
Paleo diets appeal to a different type of precision, claiming to be uniquely aligned to our supposedly unchanging genes and genetically determined dietary needs, as illustrated by the title of Mark Sisson’s book "The Primal Blueprint: Reprogram Your Genes for Effortless Weight Loss, Vibrant Health and Boundless Energy." This is despite continuing scientific uncertainty over what Paleolithic people actually ate, and the diversity of dietary patterns and cuisines that many cultures have developed—and seem to have adapted quite well to—over the past few thousand years. Paleo diets are usually high-meat, high-protein and low-carb, and exclude grains, dairy, and, of course, all highly processed foods.
Books that identify sugar as the chief culprit in the “obesity epidemic” make equally strong and definitive claims, such as David Gillespie’s "Sweet Poison" and Robert Lustig’s "Fat Chance." Lustig presents compelling scientific explanations for why fructose component of sucrose (or table sugar) promotes fat storage and insulin insensitivity and overrides the brain’s satiety signals. Given the excessive volumes of refined and extracted sugars being consumed by so many people today, it’s hard to disagree that cutting out sugar is an—or the most—important change that many people can make to improve their diets.
Yet the certainty with which these scientific claims are presented glosses over the ongoing scientific debate over the weight and health impacts of sugar consumption. Just blaming sugar for a range of metabolic disorders also ignores the many other highly processed ingredients and food products being consumed alongside—and often in combination with—sugar, such as trans-fats, other chemically modified fats and starches, and fabricated sweeteners and additives.
Food quality: The unspoken secret of weight-loss diets
Like many nutrition experts, these diet book authors have little hesitation in making precise and definitive claims regarding the health effects of particular nutrients or foods, thereby reinforcing what I call the myth of nutritional precision. These books also typically extrapolate from cellular and molecular level bodily processes to making broad and definitive claims about a particular food or dietary pattern.
All of these weight-loss diet books invariably claim to have discovered the secret of what types of foods or nutrients to eat or avoid for effective weight loss, or when to eat to them. Yet despite the apparent differences between them, virtually all weight-loss diet books have one thing in common. These books promote a diet primarily consisting of good quality and minimally-processed foods—or “real foods”—and they advise their readers to greatly reduce their consumption of poor-quality and highly-processed foods, sweets and beverages.
Much of the polemic in these books is in fact directed against the highly processed foods that now dominate the modern food supply. These are foods that have often been highly refined, reconstituted, and degraded during processing, and have many refined, extracted and fabricated ingredients added to them. These diet books potentially play an important role in increasing our understanding of how foods are produced or processed, and the potential health effects of these production techniques, thereby enhancing what I call our food-quality literacy.
The strategy they use to steer us away from these processed foods is to vilify or reduce the consumption of key foods or food groups. These eating strategies may also either explicitly or implicitly make us eat less food overall (or, if you prefer, to eat fewer calories).
However, in vilifying single nutrients or foods, these weight-loss diets also increase the nutritional anxieties of a public already suffering from the fear of bad nutrients, or the fear of not getting enough of the functional nutrients we’re now told we need for optimal health. These nutritional anxieties in turn create a demand for nutritional supplements and nutrient-fortified processed foods, based on concerns that we just can’t source enough of these nutrients from everyday foods.
The vilification of certain macronutrients, foods or dietary patterns also lacks credibility when these foods have formed the basis of apparently healthy diets of so many communities, and across many cultures and generations. A focus on food quality is an alternative to such exaggerated scientific claims regarding the health effects of particular foods, and the claim that there is one optimal dietary pattern for good health and weight management.