HOW MUCH WILL EXERCISE AFFECT YOUR WEIGHT?
If you’re starting a new exercise regime with visions of dramatically dropping dress sizes, we don’t want you to be disappointed. So here’s the truth: adding exercise to your life won’t lead to a sudden shedding of pounds – but that doesn’t mean exercise won’t help you achieve your weight loss goals. You simply need to have realistic expectations, while celebrating the many and varied ways that exercise will change your body and your life.
Let’s do an experiment. Let’s take 131 sedentary, overweight university students and split them into two groups. Both groups keep their diets the same. Group One maintains their sedentary lifestyle. Group Two add exercise to their weekly routine for 16 months. This consists of mainly walking and jogging, with the option of doing some cycling and elliptical training. They start with 20-minute sessions, five days a week, gradually building the duration of each session over six months until they complete 45-minute sessions. They also progressively increase intensity from 60 percent of their maximum heart rate at the start, to 75 percent at the six-month mark. This added exercise results in Group Two burning upwards of 400 calories per session, that’s 2000 extra calories across a week for a total of 69 weeks.
You heard that right: 2000 extra calories expended each week for 69 weeks. We won’t even recognize them by the end of the study!
Well, not so fast. Although we may anticipate that burning more calories through exercise will result in significant weight loss for sedentary overweight individuals, unfortunately that’s not the case.
I’m sure you’ve guessed by now that this study has actually been done. During this Midwest Exercise Trial (named after the participants who were from Midwest Universities) 74 out of the 131 study participants made it to the end: 33 in the Group One control group and 41 in the Group Two exercise group. Those who remained in the exercise group did a great job of adhering to their new routine – they attended 90 percent of the prescribed sessions. Calorie expenditure was monitored closely in each session, with the guys burning around 670 calories and the girls around 440 (the guys were heavier, which meant they had to work a bit harder on the treadmill). Both males and females improved their aerobic fitness (a 20 percent increase for guys and 16 percent for girls).
At the end of the study they had lost some body fat – an average of 2.9kg for the males and 4.4kg in the female group (6.4 and 10 pounds). But weight loss was a different story. The guys lost a paltry average of 5.2 kilograms (11.4 pounds) and the girls lost no weight. None. Zero!
I know the question you’re screaming to be answered: “If they burnt upwards of 2000 extra calories per week for 16 months without changing their diet, what did it do if it didn’t reduce their body mass?”
The answer to that million-dollar question all comes down to something called ‘constrained daily energy’. This theory, described by Herman Pontzer, in his fabulous book Burn, illustrates that as we evolved in our hunter gatherer past, we became experts at controlling how much energy we spend on a daily basis – meaning we do everything we can to keep it constant.
Being a hunter gatherer, as you can imagine, demands a very active lifestyle. For example, in the Hadza tribe in Tanzania, men will typically walk around 8.5 miles a day in search of game, while women will walk around 5 miles. In order to survive that lifestyle, the body must be able to control energy output so that we don’t overspend in our search for calories from food. Unfortunately for us, this can work against us during exercise.
To illustrate how entrenched this constrained energy effect is, Lara Dugas and colleagues compared daily energy expenditure of people who have sedentary occupations in industrialized countries with more active people who live in developing countries. Once the measures were controlled for body weight (the heavier you are the more energy you burn), the study found the average office worker in New York burned the same amount as an active individual in Nigeria or a hunter gatherer in Tanzania. We conserve energy as if our life depends on it, because for a long time it did.
This remarkable ability to control our energy output is what helps our body function consistently, but it is also what can make exercise frustratingly ineffective when it comes to shedding weight.
Quite simply, the most effective approach for weight loss is to balance energy usage with diet. Reducing the amount of calories we ingest and improving the quality of food we eat has far greater effect on our body mass than exercise alone.
Please hear me on this – exercise is REALLY good for you! I exercise six days a week and will continue to do so because it provides so many physical, mental and emotional benefits. And, although exercise doesn’t significantly alter the amount of energy you burn each day, it drastically changes the way you spend your calories.
When energy is scarce – like when we burn extra during exercise – non-essential metabolic processes reduce. The first of these is inflammation. Acute bursts of inflammation are an essential part of our repair and immunity response. However, prolonged chronic inflammatory responses contribute to allergies, arthritis, arterial diseases and other metabolic disorders. Exercise means we have less energy to spend on overzealous, harmful inflammatory processes and that is a huge win.
Secondly, spending energy on exercise dampens overactive stress responses. Again – a short burst of stress hormones during a crisis is good, but prolonged over production is harmful. Some reproductive hormonal activity can also be suppressed. That might not sound like a good idea – but too much activity in these areas is thought to contribute to reproductive cancers such as prostate and breast cancer.
Thirdly, numerous investigations have demonstrated that being sedentary causes us significant harm. The amount of time we spend sitting each day is a strong predictor of heart disease, diabetes, cancer and a range of other serious health problems. Although exercise alone may not result in significant weight loss, it definitely reduces the impact of our sedentary lifestyles.
And finally, people who lose weight through dieting are far more likely to keep it off if they exercise. One study on obese policemen assigned participants to dietary restrictions alone or diet plus exercise for two months. At the end of the study there was no difference in the amount of weight lost across the groups (as we should now expect). But once the intervention was over, only those who exercised maintained their weight loss.
We know weight loss is one of the main reasons people take action to improve their fitness. It’s understandable, for many years we’ve been led to believe that simply adding exercise is the secret to shedding those unwanted pounds. But the evidence doesn’t really support this.
There’s no doubt that a desire to lose weight can be a great initial motivator, but if success is measured by what’s happening on the scale it is easy for motivation to quickly wane. This is backed up by new findings* showing that when weight loss is the primary motivator we are less likely to stick with exercise but when enjoyment is the key motivator we exercise more often and for a longer term. With this in mind, it’s important that we seek exercise options that we enjoy, and have realistic expectations and celebrate the real benefits and changes to our bodies and lives due to exercise. These remarkable benefits can be much more life-changing than shedding a few pounds.
IN A NUTSHELL:
The most effective way to lose weight is to balance energy usage with diet
Exercise helps us maintain long-term weight loss
If you start exercising to lose weight you will soon discover many other benefits
Exercise can reduce harmful inflammatory responses (like allergies, arthritis, arterial diseases)
Exercise dampens overactive stress responses, and lessens the risk of prostate and breast cancer
Exercise reduces sedentary living and its associated serious health issues (heart disease, diabetes, cancer)
Exercise alleviates stress and helps us become mentally stronger and more resilient
And of course, exercise makes us fit, strong, agile and able.
*Motivational drivers of exercise: an analysis of the 2018 Global Consumer Survey (Hastings, Gottschall and Lee)