Fat or Fiction? The truth about 9 diet myths

Is breakfast really the most important meal of the day? Does fat content matter more than calories? A nutrition researcher weighs in
Adding more fruits and vegetables to your diet won't help you lose weight unless you also reduce your intake of high calorie foods. Fred Hutch file

Losing weight is hard — so it’s tempting to grab onto any promise of a diet or trick that will help you lose pounds quickly. Almost daily, we’re bombarded with news stories telling us what to eat, what not to eat, when to eat and how to eat. Some of these reports are supported by science, but others are myths, sometimes rooted in someone taking the results from one type of study and applying them to another situation entirely.

Many of these “diet tricks” came from observational studies in which researchers noted that normal-weight people differ from obese people in certain health habits. But to know whether or not these habits will cause weight loss, you need to specifically test whether people who are obese can actually lose weight if they adopt the habits. The gold standard to test these would be in a randomized controlled trial, in which people would be assigned at random to adopt the habit or to a control group that keeps their old habits. When put to this rigorous test, many of the things identified in observational studies have been found to be worthless as weight-loss tools.

Dr. Anne McTiernan
Dr. Anne McTiernan Fred Hutch file

Also, in the world of diet and weight loss, if it sounds too good to be true, it probably is. The best weight loss interventions produce an average 10 percent weight loss over six months. These programs stress reducing calories by 500 to 1,000 calories per day under what you need to maintain your weight, keeping track of what you eat, drink, and weigh, performing at least 150 minutes per week of moderate-intensity exercise (like walking) and having plans to deal with any diet-busting contingencies. So if you weigh 200 pounds, you could expect to lose 20 pounds following a lifestyle-change program. Adding an FDA-approved weight loss medication can increase your weight loss by 50 to 100 percent, but most of these drugs have side effects. Undergoing weight-loss surgery produces much larger amounts of weight loss, but it is invasive surgery and requires major lifetime changes to dietary intake after the surgery.

So, how do you sort fact from fiction? Here are nine of the most common myths — and what science has to say about them.

Myth #1: You can sleep it off.

I really want this one to be true. It sounds so easy — just sleep the recommended seven to eight hours a night, and the pounds will melt off. Unfortunately, this one just doesn’t have much science to back it up. There have been some very intriguing experiments, mostly in young men, who were observed to eat excessively the day after a night deprived of sleep. But this does not mean that getting a good night’s sleep will improve your chances of losing weight. There have been very few studies looking at how sleep might affect weight loss, and those tended to be small and therefore not definitive. In our own studies, we’ve looked at whether sleep influences the amount of weight women lose through exercise, and found that it didn’t matter if they sleep six, seven or eight hours a night.

Furthermore, women who described their sleep quality as less restful at the end of a year-long exercise program experienced more weight loss than those who said their sleep was more restful. It’s possible that sleep is just an indicator of something else going on that can affect weight loss. Melatonin, which induces sleep, may play a small role in reducing weight. Stress, which reduces sleep amount and quality, can jeopardize your attempts to change your diet and exercise patterns. So it might not be sleep that is the secret, but something else that affects sleep.

Bottom line: We don’t know whether sleep affects weight loss. But if your sleep problems reflect stress in your life, you might have more difficulty making good food choices. It might help to work on what’s causing the stress.

Myth #2: Calories don’t matter as much as carbs or fat content.

This one is so wrong. In study after study, including thousands of women and men around the world, reducing calorie intake has been key to weight loss. This is true whether calories are reduced by diet change, or appetite-influencing medications or stomach surgery. All involve calorie restriction, and all work to one degree or another. There may be a couple of exceptions to this rule. There’s some suggestion that very low carbohydrate diets can induce weight loss without severe calorie restriction. However, the long-term effects on weight are equivalent between “low-carb” and “low-fat” weight-reducing diets. Performing a lot of aerobic exercise can produce some weight loss. The amount of weight lost through exercise is small, however. For example, you’d have to take an hour’s walk to work off a white chocolate mocha drink.

Bottom line: Calories count, big time.

Myth #3: The scale doesn’t matter.

On the contrary, your bathroom scale matters very much. Several clinical trials have shown that weighing yourself regularly, such as once a day, improves weight loss and helps maintain the pounds lost. The other type of monitoring that is critical to weight loss is writing down everything you eat and drink and recording the associated calories. It doesn’t matter whether you use the old-fashioned paper and pencil method of recording your diet or use a fancy electronic app. All that matters is that you are consistent and honest. These two behaviors — weighing yourself regularly and keeping a daily record of your intake — are thought to be the most important parts of successful weight loss programs.

Bottom line: Dust off your scale and use it, frequently.

Myth #4: Eating breakfast will make you a champion in the weight-loss game.

It’s not clear how this fallacy was spread around as fact. Obesity researchers have seen that people who eat breakfast regularly tend to weigh less than breakfast skippers. However, that doesn’t mean that adding breakfast to your daily food intake will make you lose weight. Again, it’s the calories that count. If you add more calories in, you’ll gain weight rather than losing. There are a couple of possible reasons for the observed association between being a regular breakfast eater and being slimmer. People who skip breakfast may just not be hungry because they’ve over-eaten the night before. Food late at night, especially high-fat food, may not be fully digested by morning.

Or, people who eat things at night that can cause stomach upset the next morning might not want to face food right away. Finally, people who eat breakfast regularly may be better at regulating their food intake during the rest of the day.

Bottom line: Adding breakfast without reducing calories overall won’t reduce weight.

Myth #5: Increasing intake of fruits and vegetables will cause weight loss.

Unfortunately, just adding foods of any type to your diet won’t speed up weight loss unless you reduce calories from elsewhere. In the Women’s Health Initiative clinical trial with over 48,000 women, increasing intake of vegetables and fruits as part of a low-fat diet program without weight-loss goals had little effect on weight loss. However, increasing vegetables and fruit can help with reducing calories because they help make you feel fuller.

Bottom line: You have to reduce your intake of high-calorie items — fats, added sugars and refined carbohydrates — to get the weight loss benefit of adding fruits and vegetables.

Myth #6: Snacking causes obesity.

Clinical trials have directly tested whether eating food in small quantities over a day results in different weight changes compared with eating the same amount of calories in larger meals. The results show that it’s the calories that count, not when and how you eat them. In one of our clinical trials, snacking overall had no effect on success of a weight-loss program. However, women who snacked in the morning (between breakfast and lunch) lost less weight than those who were not morning snackers. We suspect that this just reflects higher calorie intake in morning snackers compared with others.

Bottom line: Snack away but keep the calorie count low. We recommend that dieters keep calories in snacks to under 200 calories.

Myth # 7: Yo-yo dieting sets you up to fail.

Repeatedly losing a lot of weight and regaining it is called “yo-yo” dieting or “weight cycling”. Doctors used to think that this pattern was bad for people’s health. However, careful reviews show that gaining and losing weight is not dangerous. My studies at Fred Hutchinson Cancer Research Center have also shown that women who have a history of weight cycling are just as successful with our weight-loss program than women who have no such history.

Bottom line: It’s better to have lost and gained than never to have lost at all.

Myth #8: Weight has to be lost slowly to avoid regaining the weight.

There’s plenty of evidence to show that quick weight loss is not detrimental to long-term weight loss and maintenance. In fact people who lose weight in the beginning of a program tend to be the ones to keep on track to lose more weight and keep it off. The very low-calorie diets (that need to be supervised by a physician) produce large amounts of weight loss. People don’t stay on the very low-calorie diets for very long, but when they transition to a typical reduced-calorie diet, tend to do very well, sometimes better than those who lost weight more slowly.

Bottom line: The hare might win over the tortoise in the weight-loss race.

Myth #9: It’s all in your genes.

If your parents were overweight and your siblings, aunts, uncles, cousins and grandparents were overweight, you could have a genetic predisposition to putting on excess pounds. But you could easily have no genetic causes of obesity in your family. That’s because body fatness is a perfect example of nature vs. nurture. If you take in more calories than you expend, you’ll most likely gain weight even if you have no one in your family who suffers from obesity. And even if everyone in your family has obesity, you’re not destined to follow them, as long as you watch what you eat and are physically active. In the future, scientists may know more about genetic influences on obesity and may be able to design treatments for people with specific genetic abnormalities.

Bottom line: For now, we’re all in the same boat when it comes to keeping the pounds off.

Dr. Anne McTiernan is a cancer prevention researcher at Fred Hutchinson Cancer Research Center and is also a physician. Her studies focus on diet, obesity, exercise, and risk for cancer development and prognosis. She is author of the upcoming book “Starved: A Nutrition Doctor’s Journey from Empty to Full” and blogs at https://annemctiernan.wordpress.com/.


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