How to manipulate your appetite hormone and why sitting at work counteract my fitness gains
Can I control hunger by manipulating my appetite hormones?
In recent years, scientists have identified a set of hormones that control eating behavior. For example, rising levels of ghrelin signal that it’s time to start eating, while rising levels of leptin tell you that you’re full. A German study in 2008 showed that even a single night of shortened sleep raises levels of ghrelin, explaining why you often crave snacks when you’re tired. Similarly, just two nights of short sleep cause a drop in the fullness hormone, leptin. The same is true if you consistently get even an hour or two less sleep than you need. So it’s not surprising that studies have found a direct correlation between how many hours of sleep you get and how thin you are.
Eating patterns can also influence these hormones. In a 2010 study, Greek researchers had volunteers eat identical bowls of ice cream in either 5 minutes or 30 minutes. (For the slow eaters, the researchers divided the ice cream into seven equal parts and fed it to the volunteers every five minutes, so that it wasn’t melted by the end of the half-hour.) In this case, although there was no difference in ghrelin levels, the researchers did observe significantly higher levels of peptide YY and glucagon-like peptide (two gut hormones that signal fullness) in the slow-eating group. This group also reported feeling more full.
Another long-standing staple of dietary wisdom is that you should eat frequently rather than cramming all your calories into three big meals. The idea is to prevent large hunger swings by keeping the levels of appetite-determining hormones in your gut relatively constant. But studies over the past half-century have reached conflicting conclusions about whether this actually works. Most recently, researchers at the University of Ottawa put 16 obese volunteers on diets with identical caloric deficits for eight weeks, publishing the results in the British Journal of Nutrition in 2010. Half of them ate three meals a day, while the other half ate three meals plus three snacks, with the total intake tailored so that each subject was burning 700 more calories than he or she consumed each day. By the end of the study, the subjects had lost an average of 4.7 percent of their starting weight, but there was no difference between the two groups. The researchers also measured the hourly fluctuations in ghrelin and peptide YY but didn’t find any significant differences between the two groups.
The University of Ottawa study suggests that snacking doesn’t have any miraculous appetite-reducing effects, but the subjects weren’t regular exercisers. If you do work out regularly, the rules are slightly different. It’s a good idea to eat something very soon after exercising—it could be either a meal or a snack, depending on your schedule. This will help you recover from the workout, and there’s some evidence that it might help you avoid overeating later.
Will sitting too long at work counteract all my fitness gains?
You’d think that spending an hour a day sweating at the gym would be enough to guarantee good health. But a 2010 study in the American Journal of Epidemiology added to growing evidence that what you do during the rest of the day also makes a difference. The researchers followed 123,000 people for 13 years and found that men and women who spent more than six hours per day sitting down were 18 and 37 percent, respectively, more likely to die during the study than those who sat fewer than three hours per day. What’s most surprising is that these risks were completely unrelated to how much exercise the subjects reported getting.
Scientists aren’t yet sure why spending long periods of time sitting down should cause health problems, but they view it as a sign that the low-intensity activity associated with simply walking around and doing everyday chores makes an important contribution to health. Research at the University of Massachusetts Amherst suggests that it can also make a key contribution to weight loss, since it’s low-key enough that it doesn’t spark hunger to compensate for the calories burned. A forthcoming Amherst study compared a group of volunteers who sat all day (they even used wheelchairs to visit the bathroom) with a group that didn’t sit down at all. Preliminary results show that the difference in energy expenditure was hundreds of calories—but the level of appetite hormones and reported hunger in the two groups remained identical.
Of course, for people who work in office settings, walking around all day isn’t really an option. Some experts recommend scheduling regular “micro-breaks” every 30 to 60 minutes, in which you stand up, stretch, and walk away from your desk for a few minutes (preferably not to the fridge). Free downloadable programs like Workrave (www.workrave.org) provide periodic warnings to remind you when to take these breaks.
Another low-intensity calorie-burning option is to replace your desk chair and use an exercise ball instead or even switch to a standing desk. A 2008 study by researchers at the University of Buffalo found that either sitting on an exercise ball or standing resulted in an extra 4.1 calories burned per hour compared to sitting in a regular office chair. Best of all, the typing rate of the subjects in the study was the same in all three cases. If you try either of these options, don’t go “cold turkey”—start with no more than a few hours a day. Also, be alert for signs of lower-back pain when sitting on the exercise ball, since the lack of support could expose existing weaknesses in stabilizing muscles.
None of this suggests that more vigorous exercise isn’t also important. For example, a 2010 University of Western Ontario study that compared low- and high-intensity activity found that easier exercise acts primarily on your heart, while harder exercise acts on your muscles. You need both your heart and muscles to be healthy, so don’t try to get away with just one of the options. In fact—and this is a message that applies in almost every aspect of fitness, diet, and health—the very best approach you can take to choosing your exercise intensity is to avoid doing the same thing every day.
CHEAT SHEET: WEIGHT MANAGEMENT
• Obese people who are physically fit are half as likely to die as thin, sedentary people. Aerobic fitness may be a better measure of health than body-mass index.
• When you lose weight, your muscles become more efficient and your metabolism slows down in an attempt to regain the weight. More vigorous exercise may avoid this “efficiency trap.”
• Cutting food intake or increasing exercise by the same number of calories produces the same amount of weight loss; however, some improvements in blood pressure, cholesterol, and other factors require exercise.
• Low-intensity exercise burns a higher proportion of fat than high-intensity exercise, but fewer calories overall. Weight loss depends on overall caloric deficit, because your body converts unburned carbohydrates to fat for storage.
• Losing weight through exercise alone is very challenging: middle-aged women had to exercise for an hour a day just to avoid gaining weight in a recent long-term study.
• If you’re consuming a low-calorie diet to lose weight, increasing the amount of protein you consume to 35 percent of calories helps avoid muscle loss.
• Aerobic exercise burns the most calories, but building muscle through strength training helps keep your metabolism high. Combine both approaches for the best results.
• To cover a given distance, running burns more calories than walking, which burns more calories than cycling. In a set amount of time, cycling burns more calories than walking.
• Eating slowly and getting enough sleep both help to control the hormones governing your appetite. Snacking between meals doesn’t appear to have a major effect on those hormones.
• Sitting all day at work can negatively affect your health, no matter how many hours you clock at the gym. Make sure to schedule regular breaks from your desk to stand up and walk around or stretch.