When it comes to healthy resolutions, fitness and weight loss top the list.

Nielsen surveys find that every New Year, 37 percent of us vow to get fit and 32 percent pledge to lose weight.

And to understand why, all you need do is scan our national health statistics — or most any American crowd.

Sadly, being overweight and obese is becoming the norm. Today, about two thirds of U.S. adults qualify as overweight — and a full one-third are clinically obese.

Aside from the damage it can cause to self-confidence — thanks to society’s focus on body shape — and even to job prospects, the health dangers of excess weight are well known.

Being overweight or obese raises the risks for these conditions and more:

  • Osteoarthritis
  • Type 2 diabetes
  • Metabolic syndrome
  • Diseases of the heart and blood vessels
  • Non-alcoholic fatty liver disease (NAFLD)
  • High blood cholesterol and triglyceride levels
  • Low self-esteem or depression, including in children

So, it may seem to make sense that getting fit and losing weight top the resolutions list.

After all, you need to exercise to lose weight, right?


Exercise undoubtedly boosts your health, energy, and sense of well-being. But when it comes to shedding pounds, exercise is a necessary — but insufficient — factor.

Diet — not necessarily “dieting” — is key
Diets and commercial diet programs that focus on calorie cutting — especially those that involve branded, pre-packaged meals — can certainly shed weight, but they're not necessarily necessary.

And new evidence suggests that debates over the relative efficacy of low-fat versus low-carb diets only serve as a distraction: see Stunning Study Upsets a Big Diet Debate

When you consider the biological factors surrounding energy expenditure, it’s easy to see the role exercise plays (or doesn’t play) in weight loss.

We expend energy in three main ways: basal metabolism (60-80 percent), digesting food (about 10 percent), and physical activity of all kinds, from hard exercise to simple fidgeting (10-30 percent).

Accordingly, most experts recommend abiding by the 80/20 rule:

  • 80% of weight loss comes from diet.
  • 20% of weight loss comes from exercise.

However, this rule comes with one caveat. Success at losing weight and reducing the proportion of body fat appears to be closely tied to the intensity of the exercise in which you engage.

So, before we look at the research regarding the effects of exercise on weight loss, we need to understand a measure of exercise intensity called “metabolic equivalents” or METs.

One MET is the energy you expend while you’re sitting quietly, therefore burning calories at what’s called your “resting metabolic rate”.

At rest, the average adult burns about one calorie per hour for every 2.2 pounds of body weight, so someone who weighs 140 pounds would burn about 63 calories while sitting quietly for an hour.

Moderate-intensity exercise is defined as any activity that equates to 3 to 6 METs — in other words, any activity that would burn three to six times as many calories per hour as sitting quietly for one hour.

Moderate exercise includes activities like brisk walking (4 mph) on a level surface, bicycling at 10-12 mph, light-to-moderate weightlifting, doubles tennis, pushing a power lawn mower, gardening, or performing relatively vigorous household cleaning (e.g., washing windows, vacuuming, mopping).

Vigorous exercise is defined as any activity that equates to 6 or more METs, such as running, walking uphill, hiking, jogging (6 mph), dancing, bicycling quickly (14-16 mph), shoveling, playing basketball, soccer, or singles tennis.

Of course, the MET measure can’t account for your level of fitness. While a brisk walk would be easy for a younger person who runs routinely, it would count as more intense for a relatively sedentary senior.

And, your resting metabolic rate depends on the proportion of muscle in your body — the more muscle you have, the more calories you burn at rest.

Studies of exercise for weight loss affirm the 80/20 rule 
We started this discussion with the 80/20 rule, which holds that diet changes can shed up to 80 percent of excess weight, while exercise can help you drop up to 20 percent.

While the 80/20 rule holds true in general, the effectiveness of exercise for weight loss can vary rather widely, depending upon the intensity or MET score of the exercise being tested.

Canadian review: Vigorous exercise shed 3x more pounds, at least in the short term
Back in 2001, researchers from Canada’s Queen’s University reviewed the clinical evidence that’d been published from 1966 to 2000, and categorized the trials as short-term or long-term (Ross R et al. 2001).

Most short-term trials involved vigorous exercise, and — compared with longer-term trials, which typically involved moderate exercise — produced three times more weight loss and reduced body fat by a little bit.

The author’s conclusions suggest that vigorous exercise sheds more weight, more quickly, than moderate workouts — a seeming case of clinical evidence upholding conventional wisdom.

We offer one note of caution. The available evidence couldn’t reveal whether vigorous exercise would continue to beat moderate exercise so clearly over the long term. If not, that would render the two levels of intensity roughly comparable, over the course of years to decades.

Seattle clinical trial: Diet plus exercise is best, and the 80/20 rule held
Six years ago, researchers from Seattle’s Fred Hutchinson Cancer Research Center published a year-long trial involving 399 overweight-to-obese postmenopausal women (Foster-Schubert KE, et al. 2012).

The women were divided into four groups:

  • Diet and exercise
  • Diet only — Calorie-reduced, low-fat diet 
  • Exercise only — Moderate-intensity aerobic exercise program
  • Control — No lifestyle interventions

These were the average weight-loss results for each group:

  • Diet-only group — 8.5 percent of weight
  • Exercise-only group — 2.4 percent of weight.
  • Diet plus exercise group — 10.8 percent of weight

And, affirming the 80/20 rule in striking fashion, the diet-only group lost 78 percent as much weight as the diet plus exercise group — just two percent off the mark!

Japanese review: Aerobic exercise sheds weight and visceral fat
In 2007, a Japanese team published their review of 16 clinical trials, and arrived at an encouraging conclusion — at least in relation to the effects of vigorous aerobic exercise.

They concluded that vigorous aerobic exercise significantly reduced both total body weight and, to a lesser extent, visceral fat (Ohkawara K et al. 2007).

Visceral fat accumulates around major organs, and is a particularly unhealthful form, tied to metabolic disorders and inflammation. Interestingly, some people in the trials under review lost a significant amount of visceral fat without losing very much total weight

The only exceptions were people with metabolic disorders, who did not achieve significant loss of total weight or body fat.

As they wrote, “These results suggest that at least 10 METs [of] aerobic exercise, such as brisk walking, or light jogging is required for visceral fat reduction, and that there is a dose-response relationship between aerobic exercise and visceral fat reduction in obese subjects without metabolic-related disorders.”

Overall, the evidence backs the wisdom of the 80/20 rule, and suggests that you shouldn’t rely heavily on exercise.

However, exercise is clearly critical — it just won’t shed very much weight unless you do it fairly vigorously and frequently.

Diet wisdom from science and tradition
Since diet remains the chief weight-loss factor, the obvious question arises.

How should we eat to shed pounds, and/or keep them off?

The evidence supports these "food rules" from author/journalist Michael Pollan:

  • Eat food. Not too much. Mostly plants.
  • Don't eat anything that won't eventually rot.
  • Don't buy food where you buy your gasoline.
  • Don't eat anything your great grandmother wouldn't recognize as food.
  • Don’t eat anything with more than five ingredients, or ingredients you can't pronounce.
  • Stay out of the middle of the supermarket (packaged products); shop on the perimeter (fresh produce, seafood, meats, etc.).
  • It's not just what you eat but how — do it slowly, and stop when you’re just starting to feel full.

We’d like to add some more evidence-based recommendations:

And, yes, get moving, whether it’s gardening, dancing, swimming or cycling.

On top of its overall health benefits, excercise provides strong support for your weight loss efforts.

You may find two of our prior reports on research in this realm useful: Does Exercise Really Shed Pounds? and Can Yoga Aid Weight Control?.



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  • Centers for Disease Control and Prevention. Adult Obesity Facts. Accessed at http://www.cdc.gov/obesity/data/adult.html
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