The 20-minute fat-burner: Try this workout from Carmichael. It varies your sprints to challenge your cardiovascular system and muscles in different ways. Following your warmup, start cycling at an intensity that's about 95 percent of your full effort for 90 seconds, followed by a 90-second recovery interval at about 40 percent of your full effort. Then, using the same intensities, perform 60-second and 30-second intervals. After the final 30-second recovery period, cycle at 70 percent of your full effort for 4 minutes, then repeat the entire set of intervals.

The popular low-carb diets (such as Atkins or Paleo) modify a true keto diet. But they come with the same risks if you overdo it on fats and proteins and lay off the carbs. So why do people follow the diets? "They're everywhere, and people hear anecdotally that they work," McManus says. Theories about short-term low-carb diet success include lower appetite because fat burns slower than carbs. "But again, we don't know about the long term," she says. "And eating a restrictive diet, no matter what the plan, is difficult to sustain. Once you resume a normal diet, the weight will likely return."
Yes, you lose weight when you cut calories, but pounds lost aren’t always fat. Some of your weight loss may also come from muscle tissue. Cyclists that diet often end up thinner, but risk becoming slower and weaker on the bike. As pioneering diet expert Covert Bailey once wrote, “When someone says that they lost 20 pounds, the key question is: 20 pounds of what?” Some dieters can end up having a higher percentage of body fat even as they lose weight. And don’t forget that muscle burns calories. The more muscle volume you have, the more calories your body can burn—even when you’re just lying on the couch.
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