What's better for weight-loss, diet or exercise? Is it true that weight-loss is 80% what you eat and 20% exercise? Why does it get harder to keep off the pounds with age? I get asked questions like these frequently, but rarely have the time to really give an answer that I believe is sufficient at explaining the answer effectively. Therefore, I'm constrained by time to give soundbite answers that are mostly correct. In today's article it is my hope to delve a little bit more deeply into what the science really says about these things and help improve awareness.
So to start things off, let me tackle the question of what is better for weight-loss - diet or exercise? Based on the principle of energy balance which explains weight-changes based on calories in versus calories out, it is safe to say that it is easier to alter the equation in favour of less calories through dietary changes. Simply think about the time it takes to burn 500 calories on the treadmill compared to how quickly they can be eaten (an hour jogging vs eating eleven Oreo cookies.)
If it's so easy to change the energy equation through eating why do so many of us still struggle with weight? This is a complicated question that researchers will probably continue to work on for years. What we do know is that by decreasing caloric intake we also slow down metabolism. While using less energy daily because of a slowed metabolism may have life-lengthening benefits, it messes up weight-loss efforts.
One of the ways that metabolism is slowed down is through the loss of lean body mass. Take for instance, the conservative estimate of every pound of muscle in the body (one of the major components of lean body mass) burning an average of 5 calories per day. So someone with a 100 pounds of muscle on their body would burn 500 calories per day just to support the demands of the muscle. When that person goes on a diet and loses 10 pounds in a month on average about 30% of that will be lean body mass or muscle and bones and so on. With the drop of three pounds of muscle this individual will now burn 15 calories less everyday. This may not sound like much but it can add up over time.
In one year a daily fifteen calorie surplus will add up to a net gain of 1 1/2 pounds of fat gain. Over a decade this would be a whopping fifteen pounds. To make matters worse this number would actually be compounded by a natural metabolic decline that occurs with age unless lifestyle modifications are in place to slow the decline,
Where Exercise Really Shines
This is why exercise is so critical to successful weight maintenance. Exercise helps to preserve muscle mass as we age. Resistance training can even increase muscle mass which can lead to modest metabolic increases over time. What's more, there is evidence that even in the presence of a low calorie diet, exercise can preserve the existing muscle mass. This is likely one of the key reasons that diet and exercise together are more effective for fat-loss than either component is alone.
Keep in mind that not all exercise is created equal. Aerobic activities tend to be better documented as having a sufficient energy output to alter body weight, but don't have the same muscle preserving and growth stimulating properties of resistance training. Thus both are important parts of a fat-loss plan. Over the long-term the metabolic effects of preserved or increased muscle mass from resistance training may very well be the more powerful factor, but in the shorter-term aerobics will absolutely boost fat burning and improve other health parameters as well.
Take a look at the possible future for our imaginary 25 year old woman named Sally.
Sally will start out at 130 pounds and having a Resting Metabolic Rate (RMR) of 1500 Calories. Now of course her total energy expenditure can deviate from the examples shown which are oversimplified, but the general patterns seen will hold true.
In this scenario Sally is going to follow the default path of age-related metabolic decline without ever taking exercise seriously and never going on diets:
Based on an average metabolic decline of 3-5 % per decade after 20 years of age we can expect Sally's resting metabolic rate to drop to 1425-1455 (average 1440) by the age of 30. Assuming Sally continues to consume 1500 calories per day but only burns 1440 calories per day, she can expect to gain six pounds of fat per year after age 30. This might not all show up the scale though because she'll also be losing muscle with age.
This time Sally is going to combat her weight issues with diets that deplete her muscle mass.
In addition to the slowing of her metabolism by 3-5% per decade as in the first scenario Sally is going to lose muscle mass by dieting each year which will actually cause her to gain weight over her lifetime. For simplicity let's say that every second year Sally goes on a diet where she loses ten pounds, but three of those pounds come from muscle. As discussed above this would add an additional 15 calorie surplus each day. Sally can expect to gain 9 pounds of fat each year after age 30 if she eats the same as she did when she was 25. This will increase by 1 1/2 pounds every second year when she repeats her diet.
This time Sally is going to do resistance training 2-3 times per week and maintain her muscle mass and preserve her resting metabolic rate as she ages.
Since muscle loss is thought to represent almost all of the age-related metabolic decline we'll estimate it reducing the decline by 95%.
Now Sally will be looking at reducing her age-related decline from a drop to 1440 by the age of thirty to only a drop of 3 calories per day to 1497. At this rate Sally will gain about 1 pound of fat every three to four years after the age of thirty.
It shows how powerful the exercise component is for maintenance!
Finally in this scenario Sally is going to combine eating sensibly with exercise. What will happen here is that Sally will be able to make mild modifications to how much she eats in conjunction with her exercise over the years and will be able to maintain a healthy weight.
What about those percentages?
It is often said that weight-loss is 80% diet and 20% exercise or sometime 70/30 and so on. The thing is that although this sounds nice and certainly promotes the importance of eating sensibly to achieve and maintain a healthy weight it's just one of many possibilities that should be based on personal needs.
Studies continually show that the combination of diet and exercise yields the greatest changes in body composition, so a combination of the two is certainly advisable. As for what percentage each plays... that is up to personal preference and need.
The take home message here is that both diet and nutrition are of extreme importance in the weight management equation. What a person eats is more likely to create faster changes, while exercise is extremely powerful at helping to maintain weight.
Bryner, R. W., Ullrich, I. H., Sauers, J., Donley, D., Hornsby, G., Kolar, M., & Yeater, R. (1999). Effects of resistance vs. aerobic training combined with an 800 calorie liquid diet on lean body mass and resting metabolic rate. Journal of the American College of Nutrition, 18(2), 115-121.
Garrow, J. S., & Summerbell, C. D. (1995). Meta-analysis: effect of exercise, with or without dieting, on the body composition of overweight subjects. European journal of clinical nutrition, 49(1), 1-10.
Hagan, R. D., Upton, S. J., Wong, L. E. S., & Whittam, J. (1986). The effects of aerobic conditioning and/or caloric restriction in overweight men and women. Med Sci Sports Exerc, 18(1), 87-94.