Exercise and Weight Loss

Much has been said about exercising to lose weight. I myself have blogged about it here and here. The general consensus seems to be that if you want to lose weight, you need to eat less and move more. This is based on the fact that in order to lose weight, we need to burn more calories than we consume. Calories in < calories out = negative calorie balance.

‘Calories in’ are basically all the things you consume, i.e. food, drink, supplements and spoon licks. ‘Calories out’ are made up of three major components: resting metabolic rate (the calories your body burns at rest), thermic effect of physical activity (non-exercise activity and deliberate exercise) and the thermic effect of eating (the energy used to digest, absorb and convert food).

It’s not easy to measure either of them, but ‘calories in’ is a bit easier than ‘calories out’. However, just because it’s difficult to measure doesn’t mean that energy balance doesn’t apply. The energy balance equation states

calories in – calories out = energy balance (weight gain/loss/maintenance).

So when it comes to weight loss, according to the energy balance equation, moving more (calories out) and eating less (calories in) makes perfect sense. Increase your energy expenditure and decrease your energy intake. However, unfortunately, it’s not quite that easy. The variables in this equation are not totally independent of each other. Let me explain.

1 Exercise decreases non-exercise activity

The factors that make up total energy expenditure (TEE) are not independent – i.e. they do influence each other. It is a widely held belief that an increase in deliberate exercise decreases non-exercise activity (that is your everyday moving such as shopping, gardening, laundry and walking). For example, the belief is if you exercise hard, then you end up spending the rest of the day on the sofa. In other words, you’re less likely to run up the stairs after a sweat session in the gym. You even fidget less.

However, there is a study by Washburn et al that conducted a systematic review of all the available studies on this belief.¹ It came to the conclusion that there is minimal evidence to support the hypothesis that prescribed physical activity (exercise) results in decreased non‐exercise physical activity (so all the other everyday moving you do like shopping, gardening, walking the dog, going up the stairs, fidgeting etc. ) in healthy adults. That’s good news!

While there is no evidence for this widely held belief to be true across all populations, it is mostly due to various shortcomings in the design of these studies. However, some results suggest that non‐exercise physical activity may decrease in response to exercise training in some populations, i.e. older individuals. All five studies that concluded this used a non‐randomized design, included primarily aerobic exercise training (as opposed to resistance training) and were conducted in sedentary overweight or obese older adults (median age of 61 years). Interestingly, the median age across all other study designs that found no evidence for decreased non‐exercise physical activity was 44 (range 29–53 years).¹ 

These results suggest that non‐exercise physical activity may decrease in response to exercise training in older sedentary and overweight individuals. 

As I have discussed previously here, losing weight is much easier for most people than keeping the weight off. The yoyo effect of dieting is a fear inducing phenomenon widely known and used as an argument that diets don’t work. When it comes to weight loss maintenance, i.e. keeping weight down, regular exercise has been shown to be a key characteristic of those who have been successful with weight loss maintenance. The National Weight Control Registry (NWCR) is the largest prospective investigation of long-term successful weight loss maintenance. Included in this registry are the behavioral and psychological characteristics of over 10,000 people who have lost at least 30 pounds (~13.6 kg) and have kept the weight off for at least one year.³ Studies based on this registry demonstrate a positive correlation between the amount of exercise completed and the percentage of maintained weight loss. Although these studies cannot definitively show that programed exercise is responsible for weight loss management, they do suggest that success is unlikely, unless regular exercise is incorporated into one’s lifestyle. 

So when it comes to losing weight, an increase in deliberate exercise doesn’t seem to lower non-exercise activity, unless you are sedentary, overweight and older. And when it comes to keeping weight off, exercise seems definitely to be part of doing so successfully.

2 Exercise increases appetite

Many studies have examined the effect of single bouts of exercise on appetite, mostly in lean, physically active males. They have found that feelings of appetite are suppressed during and right after exercise. After 30 to 60 minutes appetite perceptions go back to normal. There is no change in energy intake on the day of aerobic exercise and resistance exercise.²

When it comes to repeated, regular exercising, which is more meaningful to look at if we’re interested in exercise as a tool for weight loss maintenance, the studies are more conflicting. The findings in this scenario are inconsistent, i.e. some find increased appetite, some no change and some even a decrease in appetite. However, it has been suggested that regular exercise alters the sensitivity of the appetite control system by balancing the increased drive to eat with an improved satiety response to a meal.

As conflicting and unclear as these studies are, I believe there is one major factor why for some of us exercise doesn’t work as a weight loss tool. It’s not so much a physiological need for food (an increase in appetite), but for many, exercise is a reason to reward themselves – with a treat. As long as exercise is considered a “chore” and not a fun activity, a reward seems justified. And I don’t know about you – but I don’t need increased or reduced appetite to crave a doughnut or a piece of pizza. Unfortunately, a doughnut or a slice of pizza wipes out the calorie expenditure of a gym session pretty easily.

Whether we compensate for increased exercise by eating more (or moving less the rest of our day as explained in the paragraph above) is individual. These behaviours may be conscious or unconsciously done and vary in degree. For some individuals it may tip the energy balance equation into a surplus (resulting in a weight gain), while others keep it negative (weight loss). Studies haven’t shown yet which factors predict whether and how we compensate. There is some evidence that the following are more likely to cause compensation:

For these individuals, exercise doesn’t work as a tool for weight loss and weight loss maintenance.³

3 Eating less decreases exercise performance

This is one of the biggest problems for people who are already very lean and are pushing the boundaries as professional athletes. In certain sports, athletes need to diet down to a certain weight to make the cut or increase performance. For example, to get to a certain weight class in boxing or martial arts, or to get to a certain weight for maximum performance in bike riding or make weight for a weightlifting or bodybuilding competition. As you cut calories further and further you have less and less energy to perform at your best in training. You are simply too tired and exhausted, your body just wants to rest and conserve energy as much as possible, while you are trying to push your body to work harder.

4 Individual variability

As you can see from the discussion so far, the available research isn’t able to give us clear answers. There is too much individual variability. Clinical exercise studies report a broad range of responses in the measurement of appetite, energy expenditure, and energy balance. This inconsistency in response has led many researchers to classify research participants as exercise “responders” or “non-responders”, with the intention of studying their distinguishing characteristics. An individual’s metabolism is influenced by age, sex, body fat, insulin sensitivity, aerobic capacity and maximal fat oxidation during exercise and may also influence how physical activity impacts weight regain.³ “Blanket statements suggesting exercise will improve the maintenance of lost weight in everyone should be tempered because an individual’s response to exercise interventions will ultimately influence whether exercise is beneficial for an individual” (Foright, 87). 

5 So do I need to exercise for weight loss?

If you ask me whether you need to exercise to lose weight or maintain weight loss, I would give you the following advice:

• You don’t have to exercise to lose weight. In particular, if you have a lot to lose (i.e. you are overweight or obese), you can cut calories by eating less quite easily. Also, a lot of obese people have mobility and joint issues – exercise in this case would do more harm than good if not done properly. A lot of very overweight people also don’t like to exercise as it’s not comfortable for them to move their big bodies. I am a firm believer that exercise should be enjoyable, otherwise it is not sustainable and defeats the purpose. But you’ll have to ensure that you consume less calories than you burn.

• If you are already at a good weight and are just looking to shave off those last few kilos, then exercise would probably help a lot as it is not easy to cut calories further (let’s say your maintenance is 1500 kcal/day and you’re looking to cut another 500kcal) by eating less. Spending more energy would definitely help in this case to get to a negative energy balance.

• If you absolutely hate exercise and you cannot think of anything you like to do – even if it’s just long walks, hiking, playing football with your kids or swimming – then don’t do it to lose or maintain weight. As I said above – unless you find a certain enjoyment in exercise you won’t keep it up, which defeats its purpose.

• Notwithstanding what I just said – exercise is not meant to just get or keep us at a healthy weight. Exercise is important for our general health and wellbeing. I have written a lot about the many benefits of physical exercise, so if your goal is to become old healthily with a functioning body, then some sort of exercise should be part of your daily life. Regular exercise lowers all-cause mortality and can prevent the onset of obesity, type 2 diabetes, hypertension and cardiovascular disease.³ As I have mentioned a million times – you don’t need to go to the gym if you hate that. Find activities you enjoy and make these part of your life by making them habits (see my blog on how to do this here). Join a tennis club, ride your bike around the park, walk your dog for hours, go swimming with your friends, play basketball with your kids or grandchildren. Bear in mind that weight bearing exercise and flexibility training play a major role as we get older too.

• Exercising for weight loss maintenance is great – and not just because of the calories you burn. Having a habit of exercising – where being active is part of your lifestyle – projects a picture of yourself as a fit and healthy individual. Being active supports your overall health in so many ways and influences the way you live. You may not even notice it! While you’re active, you’re not sitting around munching mindlessly on unhealthy snacks. 

• Studies show that those who can maintain a program of regular exercise are more likely to keep weight off. There is considerable correlative data, retrospective analyses, and evidence from preclinical models of weight regain that support this statement, though we simply do not have the evidence from clinical trials to establish causality.³

6 How much exercise should I be doing?

When it comes to general health, The WHO guidelines recommend at least 150 min of moderate-intensity aerobic physical activity or 75 min of vigorous intensity physical activity per week. 

Results of the U.S. National Health and Nutrition Examination Survey (NHANES) suggest that for the maintenance of body weight, the amount of recommended physical activity is double the WHO recommendations.³ 65% of the NHANES population self-reported meeting recommendations for physical activity. However, objective measurements of physical activity using accelerometer devices demonstrated that only 5% were achieving recommended levels of activity. This is mirrored in clinical exercise studies of weight loss maintenance, where compliance is relatively poor even when substantial behavioral, psychological, environmental, and financial support is provided. Furthermore, approximately 50% of adults who initiate an exercise program drop out within the first 6 to 12 months. 

So exercise for weight loss – yes or no? In my opinion, exercise is always a great idea as long as you enjoy it. It has so many benefits in addition to weight loss. If you absolutely hate it, then don’t do it, but try to find activities you enjoy and can incorporate in your daily life. When it comes to weight loss maintenance, exercise plays a big role in doing so successfully – and again, there is much more to exercise than just keeping weight off. Exercise (an active life) should be part of our lifestyle to ensure we grow old feeling great and healthy. Just be mindful that you don’t overcompensate – so keep moving all day and don’t give in to overeating after exercise.

¹ Washburn, R.A. et al (2013), Does increased prescribed exercise alter non‐exercise physical activity/energy expenditure in healthy adults? A systematic review, Clinical Obesity, 4/1 pp. 1-20

There may be an inherent problem to randomized control trials (RCT). This may be due to the RCT design, which randomly assigns participants without taking into account their proclivity to exercise regularly. As a result, participants that may have no desire or even an aversion to regular exercise may be assigned to an exercise arm of a trial. Conversely, those who are more inclined or highly motivated to exercise may be assigned to a sedentary arm of a trial. 

² Dorling, J. et al (2018), Acute and Chronic Effects of Exercise on Appetite, Energy Intake, and Appetite-Related Hormones: The Modulating Effect of Adiposity, Sex, and Habitual Physical Activity, Nutrients, 10/9 pp. 1140ff

³ Foright, R.M. et al (2018), Is Regular Exercise an effective strategy for weight loss maintenance? Physiology and Behavior, 188 pp. 86-93 

⁴ Visona, C., George, V.A. (2012), Impact of Dieting Status and Dietary Restraint on Postexercise Energy Intake in Overweight Women. Obesity, 10/12 pp. 1251-1258

⁵ Emery, R.L. et al (2016), Examining the effect of binge eating and disinhibition on compensatory changes in energy balance following exercise among overweight and obese women. Eating Behaviors, 22 pp. 10-15