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7 Diet Rules Science Says You Should Stop Following

What we think we know about snacking, carbs, and exercise is mostly wrong.

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When it comes to managing one's weight, I don’t know anyone who wouldn’t like a few easy rules to follow. For example, if you told me that if I just cut chocolate out of my diet and then I’d have Sports Illustrated calling to feature me on the cover of the swimsuit issue, I’d stop eating chocolate … well, at least for a little while. The problem is that most of our diet "rules" don’t actually work. And even if they do work for a while, they aren’t sustainable. (Do you really want to never eat chocolate ever again?)

Here are some of the misleading rules we hear most often—and the science that explains why you should ignore them:

  1. Don’t Snack Between Meals. This is one of the oldest diet rules around. The idea is to eat three square meals a day and then don’t eat otherwise. So, what’s the problem? For one, if you are hungry, and don’t have a snack between lunch and dinner, you’re more likely to overeat at dinner. In other words, any calories you “save” by skipping a snack are quickly made up (usually, plus some extra) during dinner. The other problem with this rule is that it essentially forces you to have three meals during specific times of the day. But what if you don’t feel like breakfast when you wake up at 6:00 am, but you are hungry for breakfast at 9:00 am? Should you force yourself to eat breakfast when you wake up and not snack once you get to work? Although it's practical for us to eat according to some mealtime conventions, it’s not a good idea to ignore our bodies’ signals of hunger and satiety (i.e., fullness). In fact, classic studies of eating-disorder and obesity patients make it clear that maladaptive eating patterns can result from ignoring our bodies when they are trying to tell us that they need food. And chronic dieters (sometimes called “restrained eaters”) who make it a habit of ignoring their bodies’ hunger signals often find themselves ultimately having a difficult time determining when they are actually hungry. Your best bet: Snack when you feel hungry, but choose healthy options like fruit and veggies.
  2. Wipe White Out of Your Diet. Remember when carbs—bread, pasta, rice—were the base of the food pyramid? Then, Dr. Atkins’s diet revolution began and by the late '90s everyone looking to lose weight was afraid to eat bread. It’s true that a lot of “white foods”—white bread, white pasta, white rice—aren’t particularly nutritionally dense, but they fill you up fast (as do most carbs) and they often aren’t as bad as they’ve been made out to be. Eliminating carbohydrates from our diets means eliminating foods that retain water, typically allowing for a quick initial drop in weight. And who doesn’t love that? And skipping carbohydrates, the body’s primary source of easily accessible energy, sends the body hunting for different sources, including utilizing fat stores for energy, resulting in a reduction of fat (and body weight). All of this is well and fine, but what happens when you really want a roll with your dinner? If you want to lose weight by excluding carbs, then you have to realize that when you add them back into your diet you’re going to gain back some of the weight you’ve lost. So maybe a better approach is to be more moderate—no need to wipe out all of the white, but do your best to reduce some carbs and replace the white with browner, grainier, more nutritional alternatives.
  3. Fasting Will Help You Lose Weight Fast. If you eat less than you usually do, you’re very likely to lose weight. So if you stop eating all together you should lose a ton of weight, right? But hold on—this logic isn’t completely sound. When you stop eating, your body goes into “starvation mode,” your metabolism slows down in order to utilize whatever food it has available, and your weight loss will slow down. Of course, if you (partially) fast for many days or weeks, you will lose weight. And if you do it longer term, you will lose a lot of weight, but also increase your risk of heart failure, brittle bones, muscle loss and weakness, fainting, dry hair and skin, hair loss, and even death. Such an approach typically results in the diagnosis of an eating disorder—often referred to as the most deadly of all psychological disorders. If you aren’t convinced yet of why this is unwise, consider: You can eat healthy portions of nutritious foods every day and lose weight in a gradual, sustainable manner. Or you can fast, feel very hungry, not necessarily lose weight all that quickly, and jeopardize your health. Easy choice, right?
  4. Exercise is the Best Way to Lose Weight. There are countless reasons to exercise: It benefits your psychological health, your physical health, and can help you live longer. You can also exercise your way into a skinnier pair of jeans, but it’s not the easiest or the best way to drop pounds. Why? To lose weight and stay slim, you’re also going to need to maintain healthy eating habits. There’s no getting around the fact that it is easier to consume calories than it is to exercise them off. Nutritional science and exercise physiology are extremely complex, but just think about the basic math involved: If you run for 30 minutes at a pace of 10 minutes per mile (or, in other words, 3 miles), you will burn approximately 300 calories. However, a pumpkin spice latte from Starbucks contains about 300 calories. So, if you have a good run and reward yourself with a latte later that day, it’s easy to see why you won’t be losing much weight.
  5. Skinny Foods Make You Skinny. Skinny cow desserts. Skinny water. Skinnygirl margaritas. There is no shortage of foods that claim to make you “skinny.” Of course, it isn’t actually this simple. Plain water is calorie-less, while margaritas and desserts are nutritional indulgences. No “skinny” dessert on its own will ever help you to lose weight. These foods and drinks are often heavily processed, with plenty of added ingredients, such as acesulfame potassium and sodium benzoate, which have questionable safety track records. Perhaps just as worrisome are the psychological effects of eating something that you think is a “skinny" food. People often overeat when they think that a food is “low-fat” or “diet” even if the food is nutritionally quite similar to the “regular” version (as it often is). Michael Pollan has referred to this as the “Snackwell’s Phenomenon.” Snackwell’s are a brand of cakes, cookies, and other sweet (and primarily non-nutritive) foods that have capitalized on this marketing strategy and become very popular. The problem is, people are more likely to eat two Snackwell’s cookies (at 150 calories each) because they are advertised as a “diet food,” than they are to eat one regular homemade cookie, which has 200 calories. Not only does this result in an extra 100 calories, but it also likely causes you to be much less satisfied with your dessert.
  6. Skip Dessert. A good dessert—chocolate cake, ice cream sundae, chocolate chip cookies—is devoid of nutritional value. They all contain fat, sugar, and little else. So there is really no reason to eat dessert, except that it tastes awesome—and because passing up dessert today may lead you to overindulge on sweets tomorrow. Don’t believe me? Consider the evidence from a recent study in which half of the participants were allowed a regular breakfast (300 calories) but the other half were given a large breakfast that contained something sweet (600 calories, with some calories coming from healthy foods and some coming from a donut, a piece of chocolate, or a biscuit). The group not allowed a morning sweet initially lost weight but were unable to keep the weight off long term. By contrast, the people in the “dessert for breakfast” group gradually, but consistently, lost weight after four months on this diet (the other group started to regain weight loss after four months). These findings don’t necessarily suggest that cake for breakfast is the healthiest or most efficient route to weight loss. But they demonstrate is that it is not necessary to restrict yourself entirely from sweets. Keeping your sweet tooth under control with moderate indulgences may be the best long-term approach.
  7. Don’t Eat After 8 p.m. The logic behind this rule is that if you eat at night, you won’t be moving after you eat—you’ll be sleeping—so you won’t burn any of the calories that you’ve consumed. Turns out, your body burns calories whether you are awake or fast asleep. And if you are hungry at night and don’t eat, you’re only going to wake up hungry, leading you to eat more in the morning. In rare cases, people who avoid eating in the evening when they are hungry even develop sleep-related eating disorders and find themselves sleep-eating (similar to sleepwalking). At the end of the day, what really matters is your total caloric intake across the day (and across weeks and months), not when those calories were ingested. So, if you want a snack at 9 p.m., go for it.

Preorder Dr. Markey’s book, Smart People Don’t Diet: How Psychology, Common Sense, and the Latest Science Can Help You Lose Weight Permanently, on Amazon, Barnes and Noble, or Follow me on Twitter @char_markey or on Facebook.

Copyright Charlotte N. Markey, 2014.


Garfinkel, P. E. (1974). Perception of hunger and satiety in anorexia nervosa. Psychological Medicine, 4, 309-315. Ogden, J. & Wardle, J. (1990). Cognitive restraint and sensitivity to cues for hunger and satiety. Physiology and Behavior, 47, 477-481. National Eating Disorders Association. (2014). Anorexia Nervosa. Retrieved from: Michael Pollan and ‘in defense of food: The omnivore’s solution’. Bates Contemplates Food. Retrieved from: Jakubowicz, D., Froy, O., Wainstein, J., & Boaz, M. (2012). Meal timing and consumption influence ghrelin levels, appetite scores and weight loss maintenance in overweight and obese adults. Steroids, 10, 323-331.
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