Introduction
SOMETIMES BIGGER IS BETTER
My literary agent told me that no one wants a fat diet book. They want it to be as slim as they envision their future selves. Sorry to disappoint, but I couldn’t help it. I wanted to document every evidence-based tip, trick, tweak, and hack to give people every possible advantage—whether you’re obese, overweight, or just wanting to maintain your ideal weight.
In How Not to Diet, I cover everything from cultivating a healthy microbiome in your gut to manipulating your metabolism through chronobiology, matching meal timing to your circadian rhythms. Every section could have been a book in its own right. We certainly attempted book-length research on each subject and then tried to distill down the most compelling, actionable takeaways from each of the most promising strategies. To that end, this is really more like forty books packed into one. For those of you now wielding a physical copy of the book and thinking, This is the compact version?, take comfort in the fact that you can use it to curl for a little extra resistance exercise.
It was important to me to include all the details so you can make as informed a decision about your health as possible, but you can always skip down to the summaries at the end of each section for my take-home suggestions. I wanted to be sure to clearly articulate how I arrived at each recommendation, because I don’t want to be anyone’s diet guru. I don’t want you to take anything on faith but rather on evidence.
In the References section, I’ve included a website address and a QR code for the full list of the nearly five thousand citations referenced throughout this book. The advantage of presenting them online for you (beyond trimming five hundred pages and saving a few trees) is that it allowed me to hyperlink each and every citation to take you directly to the source, so you can download the PDFs and access the original research yourself.
Some of my conclusions are scientific slam dunks, but others are more uncertain, and I try to make the distinctions clear. That way, you can make up your own mind when trying to decide whether to incorporate any particular piece of my advice into your life. If you find yourself unconvinced by the data presented to support a particular recommendation, don’t do it. The benefit of laying it all out is that you can decide for yourself. As famed scientist Carl Sagan (who also happened to be my next-door neighbor at Cornell!) put it: “Science by itself cannot advocate courses of human action, but it can certainly illuminate the possible consequences of alternative courses of action.”9
WHAT ARE YOUR DIGITS?
Before we dive in, what does it really mean to be overweight? Obese? In simple terms, being overweight means you have too much body fat, whereas being obese means you have way too much body fat. In technical terms, obesity is operationally defined as a body mass index (BMI) of 30 or more, while being overweight means you have a BMI of 25 to 29.9. A BMI between 18.5 and 24.9 is considered “ideal weight.”
Calculating your BMI is relatively easy: You can visit one of the scores of online BMI calculators, or you can grab a calculator and calculate it on your own. To do so, multiply your weight in pounds by 703. Then divide that twice by your height in inches. For example, if you weigh 200 pounds and are 71 inches tall (five foot eleven), that would be (200 × 703) ÷ 71 ÷ 71 = 27.9, a BMI indicating that you would be, unfortunately, significantly overweight.
In the medical profession, we used to call a BMI under 25 “normal weight.” Sadly, that’s no longer normal. Being overweight became the norm by the late 1980s in the United States10 and appears to have steadily worsened ever since.11
ISN’T A CALORIE A CALORIE?
Now that we see where the lines are drawn in the weight spectrum from optimal to obese, let’s review some basic assumptions. The notion that a calorie from one source is just as fattening as a calorie from any other source is a trope broadcast by the food industry as a way to absolve itself of culpability. Coca-Cola even put out an ad emphasizing this “one simple commonsense fact.”12 As the chair of Harvard’s nutrition department put it, this “central argument” from industry is that the “overconsumption of calories from carrots would be no different from overconsumption of calories from soda.”13 If a calorie is just a calorie, why does it matter what kinds of foods we eat?
Let’s take the example of carrots versus Coca-Cola. While it’s true that in a tightly controlled laboratory setting, 240 calories of carrots—ten carrots—would have the same effect on calorie balance as the 240 calories in a bottle of Coke,14 this comparison falls flat on its face out in the real world. You could chug down those liquid calories in less than a minute, but eating 240 calories of carrots could take you more than two and a half hours of constant chewing. (It’s been timed.15) Not only would your jaw get sore, but 240 calories of carrots is about five cups—you might not even be able to fit them all in your stomach. Like all whole plant foods, carrots have fiber, which adds bulk without adding net calories. What’s more, you wouldn’t even absorb all the carrot calories. As anyone who’s eaten corn can tell you, some bits of vegetable matter can pass right through you, flushing out any calories they contain. A calorie may still be a calorie circling your toilet bowl, but it’s not going to end up on your hips.
A more relatable comparison might be something like Cheerios versus Froot Loops. As Kellogg’s is practically giddy to point out, its Froot Loops cereal has about the same number of calories as its rival’s health-hallowed Cheerios. So why does Toucan Sam get singled out? (I was deposed as an expert witness in a case against sugary cereal manufacturers, so I heard these arguments firsthand.) Yes, the two cereals may have similar calories, but that doesn’t take into account all the appetite-stimulating effects of concentrated sugar.16 In an experiment in which children were alternately offered high-versus lower-sugar cereals, had they eaten more Cheerios than Froot Loops, they could have gotten more calories, but the opposite happened. On average, the kids poured and ate 77 percent more of the sugary cereal. So even with comparable calorie counts, sugary cereals may end up nearly doubling caloric intake.17 In a lab, a calorie is a calorie, but in life, far from it.
Even if you eat and absorb the same number of calories, a calorie may still not be a calorie. As you’ll learn, the same number of calories eaten at a different time of the day, in a different meal distribution, or after different amounts of sleep can translate into different amounts of body fat.
It’s not only what we eat but how and when.
And the same number on the scale can mean different things on different diets or in different contexts. You could be losing weight but actually gaining body fat if your body sheds water and muscle mass. So it’s not just about calories in versus calories out, eating less, and moving more. We’ll see an illustration of this later, with a famous series of studies on prisoners in Vermont that showed that, depending on what the researchers fed them, it could take up to one hundred thousand more calories to create the same amount of weight gain. So you’ll learn how they effectively made one hundred thousand calories disappear. But I’m getting ahead of myself.
A DETECTIVE STORY IN FOUR PARTS
In part I, the book starts with an outline of our growing problem with obesity—the causes, the consequences, and the solutions tried to date. It answers questions such as: What led to the explosive increase in obesity starting in the late 1970s? Is being overweight really as bad for your health as “they” say? And what about the safety and efficacy of nonlifestyle approaches, such as stomach stapling, diet drugs, and weight-loss supplements?
Then, in my attempt to build the optimal weight-loss strategy from scratch, I spend part II exploring all the key ingredients that might go into creating the ideal recipe for losing body fat. In part III, we see how all the diets out there stack up against this list of criteria, and we piece together the foremost formula for healthy, sustainable weight control. You also get the tools to be able to assess all the newer-than-new diets that haven’t even come out yet.
After that come the boosters. In part IV, I unveil all the tricks and tweaks for fast-tracking weight loss that I’ve found through my years of scouring the medical literature. These are ways in which any diet can be modified to maximize the dissolution of body fat. I arrange the boosters in a simple daily checklist so you can pick and choose a portfolio of techniques that works best for you. I have to warn against skipping to this section and going for the quick fixes while continuing to eat the same crappy foods. Though there are indeed different ways to eat the same foods to achieve better results, the boosters are strictly meant to be adjuncts to a healthy diet.
In the final section, I lay to rest all the burning questions on burning fat: What are the best ways to exercise to achieve maximum weight loss? How can you safely boost your metabolism? What is the optimum amount of sleep? What does the science say about ketogenic diets, intermittent fasting, and high-intensity interval training? I also introduce you to specific foods that double as fat blockers and fat burners, and starch blockers and appetite suppressants. And did you know that the different timing, frequencies, and combinations of foods can also matter? There’s even a food that can prevent the metabolic slowing that your body uses to frustrate your weight-loss attempts.
Skeptical? You should be! I was too.
I went into this thinking I would just end up railing against all the gimmicky snake oil out there and put out much of the same standard advice on trimming calories and hitting the gym. I imagined what would set this work apart would be its comprehensiveness and strict grounding in science. I figured this book would distinguish itself—but more as a book of reference than revolution. I certainly never thought I’d stumble across some novel weight-loss strategy. I just didn’t realize how many new paths would be opened up by our newfound transformations in understanding of so many fields of human physiology. It’s been thrilling to weave together all these cutting-edge threads to design a weight-loss protocol based on the best available evidence.
This has been a mammoth but joyful undertaking. People sometimes ask me why I don’t go on vacations or even take a day off. I have to explain that I feel as though my entire life is a holiday. I feel so blessed to be able to dedicate my time to helping people while doing what I love: learning and sharing. I can’t imagine doing anything else.
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