The Role of Exercise in Weight Loss: Part 2

Part 2 of 3.

Part 1

Recently, we looked at some research that supported the observation that despite hours of exercise each week, many people do not transform their physiques for the better.

This observation formed the basis of Reality Check #1: Exercise Alone does NOT produce weight loss. Subsequently, we had to question why bother with exercise at all, if dieting drive weight loss?

Although the conventional approach to dieting, drastic caloric restriction, typically induces weight loss, many dieters have learned that diets only tend to work for a very short period of time.

Whether your diet of choice is low-carb, low-fat, grapefruit, or cabbage soup, they all seem equally effective at producing weight loss in the short term.

Unfortunately, this loss of body mass is transient and after a few short weeks weight loss often comes to a screeching halt; leaving dieters frustrated and asking themselves, “Where did I go wrong?”

Truth be told, your hormonal and metabolic systems are designed to keep you relatively weight stable. When you gain a couple of pounds, normally your appetite should be suppressed and your metabolic rate would increase, allowing you to drop the weight.

Conversely, in response to you losing a few pounds, your metabolic rate slows down and your appetite increases to encourage you to gain the weight back.

As frustrating as it may be, a fundamental property of human physiology is this: we are not designed for aggressive weight loss!

Therefore, when sustainable weight loss is your goal, you need to take steps to overcome the natural checks and balances built in to your physiology.

[Author’s note: it is supposed to be equally difficult for adult humans, outside of pregnancy, to gain more than a lbs or two of fat a year. Sadly, we are much better at overriding that control system, but that’s a topic for another day.]

While dieting can produce a desirable loss of body fat, it often has the nasty side effect of also causing a loss of muscle mass, which is not at all what you want.

Losing too much muscle tends to have a negative impact on your basal metabolic rate, which is the amount of calories you burn at rest.

Once metabolic rate decreases, weight loss becomes exceptionally difficult. Making matters worse, a sluggish metabolism often means that once you return to a “normal” eating pattern, you will more than likely gain back all the weight lost and more!

While part of avoiding the dreaded weight regain requires establishing a healthier long-term relationship with food, a significant component involves taking the right approach to training during the diet itself.

But unlike everything you’ve been led to believe, aerobic training is not a dieters best friend!

Although aerobic training does burn calories, it is nowhere near as effective for weight loss as simply eating fewer calories. It takes a solid 30 minutes of running on a treadmill to burn 300 calories, whereas it takes you less than 30 seconds to eat a 300 calorie chocolate bar.

In the interests of your time and sanity, does is not make more sense to watch what you eat as opposed to spending two hours a day on the treadmill?

But watching what you eat isn’t enough, as we’ve already established that dieting can cause a loss in muscle mass. Therefore, when we are dieting, we need to do everything in our power to protect our muscle mass and metabolic rate.

And what’s the best way to protect muscle mass?

Lift heavy things!

In fact, it forms the basis for:

Reality Check #2

During a diet, the majority of your training should be resistance training

Quite simply, resistance training protects metabolism, even in the face of drastic caloric restriction.

Don’t believe me?

Let’s look at the data.

A recent study was published investigating the effects of resistance training while dieting, in a group of older individuals.1

Over this 10 week study, older (mean age of 67 years), overweight individuals were placed into one of two conditions.

  1. Diet alone: a 10% reduction in total calories
  2. Diet + exercise: same reduction in calories + 3 full body resistance training sessions

And what was found was nothing short of amazing!

After 10 weeks, both groups lost weight, with the diet + exercise group losing more.

Before we start doing cartwheels, let’s acknowledge that the energy deficit between the two groups wasn’t identical.

So for now, all we we can say is that both diet and diet + weight training result in significant weight loss.

However, when we compare losses in fat mass to changes in lean mass, stunning results emerge.

Almost all the weight lost in the diet only group came from lean mass, which is the worst possible outcome from a health perspective. In contrast, the diet + resistance training group gained muscle and lost fat, which is ideal!

From these results, it would suggest that dieting alone is a terrible choice, at least for older individuals. But is just dieting as detrimental for younger individuals?

A study published in 2008 addressed this very question2. This study looked at a group of 94 overweight females (age: 35 years, BMI between 27-30 kg/m2), who were split into 3 experimental conditions.

  1. Diet only
  2. Diet + aerobic exercise: 3x/week; up to 40 mins per session
  3. Diet + full body resistance training: 3x/week; 2 sets of 10 reps on 10 exercises

The goal in each of the groups was to reduce their BMI to 25 kg/m2, which required an average weight loss of 12 kg.

Admittedly, using BMI is a little shortsighted, but I didn’t design the study. Another absurd aspect of this study was that all the participants were placed on a strict 800 kcal/day diet, in order to produce the 12 kg weight loss.

Although I question the use of such a low calorie diet, ultimately it did work because most of the participants were able to lose the weight in ~21 weeks.

At the conclusion of the intervention, some interesting body composition changes were found.

*In reporting their data, these researcher subdivided the women into women of African American (AA) descent and European American (EA) descent, to detect potential genetic patterns of weight loss*

First the good news; younger people seem to be able to lose body fat on a diet, without it all coming from muscle tissue.

Another good thing is that once again, we see that the only intervention group that protected muscle mass over the course of the diet was the group that performed resistance training. Not surprisingly, the researchers also found this group to have a better preservation of resting metabolic rate.

Unfortunately, both groups of women in the diet only group lost a significant amount of muscle mass, whereas European American women also lost quite a bit of muscle while in the diet + aerobic training group.

Why African American women didn’t is unclear; however the general conclusion is that most people will lose some muscle mass on a plan consisting of either a diet or a diet + aerobic exercise.

Hopefully by now you are realizing just how short-sighted is is to obsess about the scale while dieting. If too much of your body weight losses are due to muscle mass, the long-term ramifications of that diet attempts are bound to disappoint.

Thankfully, both of these studies show that performing resistance training during a diet, even a drastic calorie reduced one, enables you to preserve your muscle mass.

Therefore, for anyone interested in transitioning out of a diet with a minimal amount of weight regain, dedicating a good portion of your training time to resistance training just makes sense.

In parting, I’ll leave you with one observation. Considering that the diet + aerobic exercise group in that last study didn’t lose a greater amount of weight, nor did they lose weight at a faster rate than either of the other groups, should we question how valuable aerobic training is for weight loss.

Could it be that in the presence of a properly designed diet program, additional aerobic training has negligible benefits?

Debate that question for a bit and I’ll be back soon with more posts!


1. Avila et al. (2010), Effect of moderate intensity resistance training during weight loss on body composition and physical performance in overweight older adults, European Journal of Applied Physiology, February 2010

2. Hunter et al. (2008). Resistance Training Conserves Fat-free Mass and Resting Energy Expenditure Following Weight Loss. Obesity, 16, 1045-51.