‘Tis the season to begin exercising more, eating less, and losing weight. For guidance, the British Journal of Sports Medicine recently published “Exercise and diet in weight management: updating what works.”
The research authors said their goal was to provide a “concise summary” of scientific evidence on the topics. Below, you’ll find my summary of their summary. I hope you find it useful. If you want just the executive summary, it goes something like this:
1. Changing your food behavior (diet) has a much bigger effect on weight loss than exercise.
2. But exercise helps, and the more (and harder) the exercise you do, the bigger the weight-loss payoff. Especially over the long term.
3. Even if exercise doesn’t help you lose much weight, it makes you much healthier. So it’s basically a no-brainer.
Does exercise alone help you lose weight?
1. Not much–perhaps 2 pounds in 16 weeks is a typical result.
2. However, if you’ve got time to walk 2 hours a day, you’ll do better than this.
Does diet alone help you lose weight?
1. Yes, it can be quite powerful–leading to weight loss as high as 24 pounds in 15 weeks.
2. Of course, many regain much of this lost weight after 6 months or so.
3. This may happen because their weight loss causes a loss of muscle and a corresponding decrease in daily metabolism.
4. High-protein diets might retain more muscle mass, and decrease appetite. Thus, they tend to work well in the short term.
5. Fat restriction works in the long term. Successful members of the National Weight Control Registry maintained a 30-pound weight loss for more than 5 years by reducing their fat intake to less than 25 percent of total calories. (They also exercised a lot.)
What about exercise plus diet?
1. Combining the two might add 20 percent to your weight-loss success.
2. So you can think of diet and exercise as 80/20 contributors to weight loss.
3. The true “fat burning zone” (where the most total fat is burned) occurs at 70 to 80 percent of your max heart rate. This is a typical EZ day training effort for most runners, roughly 2 minutes/mile slower than your 5K race pace.
Does strength training help?
1. Possibly. But there’s not much supportive evidence.
What about exercise intensity, ie, going hard vs going easy?
1. There’s modest evidence that high-intensity exercise increases weight loss vs. low intensity.
2. There’s little evidence that 30 minutes a day of walking and other low-intensity exercise will have much effect on weight.
3. Walking is nonetheless a great exercise choice for people who might not be able to do more than walk. But as their weight drops and their fitness increases, they should add more intense workouts.
Should weight-loss programs be slow and steady?
1. Maybe not. Everyone advises slow and steady, but some research supports fast early losses.
2. This approach probably works because it provides a bigger initial psychological boost, which encourages continued high motivation.
What about non-weight-loss benefits of exercise?
1. They’re very important. A modest improvement in fitness can decrease your mortality risk by 20 to 30 percent. A big fitness improvement can double this.
2. That’s why exercise is always a worthwhile investment. It makes you healthier and more energetic even if you don’t lose much weight.