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Exercise, Depression and the Energy Hypothesis

January 7, 2016

There’s an increasing body of evidence claiming that exercise can help alleviate symptoms of depression. Some studies are claiming that exercise is just as effective as prescription antidepressants, and possibly even more so. The question I ask myself is: why is exercise helpful in cases of depression? It’s universally accepted that exercise is good for you in many respects. So much so, that we rarely stop to ask ourselves why that might be.

I’ll begin by saying that depression is a complex phenomenon. I don’t personally believe that depression is some one disease or disorder with some fixed set of symptoms or some single cause that we can point to. Rather, I believe it’s an umbrella term that we generally use to describe the experience of people who experience persistently low moods and a lack of energy or motivation for what seems like an abnormally long amount of time. In this post, I’m going to focus on one component or symptom of depression which is known as motivational anhedonia, this is the loss of desire or motivation to engage in activities.

It seems that one of the areas where exercise is most helpful is in helping people find more energy and motivation. I’m going to propose a simple hypothesis as to why that might be, which is that your brain has evolved to save and accumulate energy. It wants you to stay alive and hopefully spread your genes, but ideally, it wants you to do this while spending the least amount of energy possible. Your brain would rather have you accumulating energy than spending it. Body fat is an insurance policy: saved up energy to safeguard you against the bitter famine that might be just around the corner. The reason why many people find it so difficult to lose weight is likely that our brains don’t really want to let us do so.

When the winter comes around, and the days get shorter, many people experience Seasonal Affective Disorder (SAD), which can cause lower moods and difficulty getting out of bed in the morning. Here’s the thing though: it’s probably natural for you to feel tired, to move less and to spend more time sleeping during the winter. Most other mammals probably feel just the same way. This is simply your instinct trying to keep you from running around and jumping everywhere, trying to make you save your energy, because in the winter, there’s much less food for you to find. Sleeping more and moving less might not feel very good, but it’s probably the safe thing to do when resources are scarce.

How does exercise fit into the picture? I propose that your motivation to move around and do things reflects your brain’s willingness to let you spend energy. I propose that probably, somewhere in your brain, there’s some mechanism which measures how much energy you need to spend to stay alive, a kind of daily energy budget. This energy budget is likely based on how much energy you’ve needed to stay alive in the past. Exercising involves forcing yourself to spend more energy than usual. When you do this, your brain estimates that your life situation requires you to spend more energy to stay alive, and increases your energy budget.

This hypothesis might help explain why, despite the abundance of food and entertainment found in western societies, depression is on the rise. By many accounts, living conditions in North America are more comfortable than they’ve ever been. Maybe that’s part of the problem though. Maybe the comfort of modern civilization: cars which can get us around without walking, entertainment we can enjoy while sitting on the couch and microwaveable food we don’t even need to cook, have made our lives too easy. These things have made it possible for us to survive without spending energy or moving very much. Maybe, for many people, the way to find more energy is to spend more energy.

Interestingly, there’s also been some recent research suggesting that intermittent fasting, and ghrelin (the hormone which produces the feeling of hunger) might stimulate neurogenesis. As such, it’s possible that intermittent fasting might help combat depression. This also fits with the energy hypothesis, in that when there is a calorie deficit, and energy sufficiency isn’t guaranteed, the brain becomes motivated to have us spend energy so that we might be able to find more food.

I’ll conclude by saying that I do not, in any way, mean to trivialize depression, or the suffering that’s involved. I’ve been depressed, and I know very well that the last thing you feel like doing, when it seems like your world is crumbling down, is to hop on a threadmill and run. I also know that the last thing you should tell a depressed person is to “just snap out of it”. If you have a depressed friend, and you want to help them, then my advice to you is to offer them support, kindness, and a lot of patience. Lastly, exercise and diet can only go so far. Depression is not one disease, and exercise is not some universal cure. Some people cannot get out of depressed states without the help of professionals and prescription antidepressants. These people need help and support just as much.

From → Biology, Psychology

  1. Brian permalink

    Nothing magical or unknown about the effective of exercise helping depression, its called endorphins and adrenaline! In fact they can be so powerful you can become an exercise addict!

    Of course depression can take many forms – but the type of depression that most of us may encounter will certainly be reduced if not fixed by exercise.

    Fasting also works, as your body is getting new messages that are getting close to primitive motivations, like go hunting or die which for most people override higher limbic system depression types of response, like grief or other negative emotions.

    Perhaps we did to ditch expensive councillors and employee a few more Sergeant majors!

    • I don’t think “it’s the endorphins” constitutes a sufficient explanation as to why exercise might help people get out of depression. Endorphins, being natural opioids, explain why some people get a “runner’s high” after intense exercise, but that isn’t really an explanation as to why regular exercise would make you more energetic in the long run. Beta-endorphins have a half-life of just 37 minutes in humans. They are out of your body shortly after you’re done working out, and they don’t explain medium or long-term effects on their own.

  2. Kyle permalink

    I’d like to point out myself as a counterexample to your hypothesis. Due to chronic illness, my energy requirements (how much energy I spend to simply stay alive) are much higher than normal. To simply maintain my weight, my food intake is at least 3000 calories per day — that increases during periods of exacerbated illness.

    Despite my increased energy budget, my energy level is lower than healthier friends who don’t exercise, and much lower than friends who do exercise. My disposition also leans toward depression more than the people around me, even though I constantly spend more energy simply to exist.

    Of course the negative effects of illness could cancel the positive effects of a higher energy budget that you propose, but overall I don’t think a calorie deficit (alone) could explain how exercise increases energy or improves motivation.

    • You haven’t specified how you spend this energy, what causes you to need 3000 calories a day, whether or not it’s because you’re doing hours of intense exercise daily. The hypothesis I stated is about an energy budget for physical activity, based on how much activity you’ve been doing. I said nothing about increased metabolic needs.

      Apart from this, like I said, there is no one cause or one cure for depression. There are many metabolic, hormonal and neurochemical factors which can cause someone to experience anhedonia. It’s obviously not the case that everyone who experiences anhedonia is “just not doing enough exercise”.

  3. Kurt permalink

    An interesting study would be comparing depression levels in modern cities with widely varying excise levels. For example a typical North American city where most people drive like Boston Versus Copenhagen where many people bicycle. NYC might be any interesting one also. Over 50% of the people commute by subway, walking at the beginning and end of the commute.

    Another area to look at might might be standing versus sitting. Standing Desks. From the Boston GLobe: “Sitting at work is bad, but is standing actually better?”
    “In a June study, 28 office workers who were given a sit/stand desk for a month reduced their time spent in a sedentary position by 38 minutes a day compared to when they used a traditional desk. They also reported a mood boost, increased energy, and reduced fatigue.”

    Another area to look at might be Life Expectancy studies, Blue Zones, etc. One very interesting group is the Seventh-day Adventists. Ignore the religion and examine their life style choices. “On average, Adventist men live 7.3 years longer and Adventist women live 4.4 years longer than other Californians”


  4. Dionysius permalink

    To be healthy is to be happy. The brain is an organ just like any other organ, and to function optimally, it needs a healthy body to live in. Prolonged periods of inactivity make the body go into a “less-alive” state. Perhaps there is an evolutionary memory in the brain/body that associates prolonged inactivity with the idea that resources are scarce (you’re huddling in a cave, not hunting/gathering) and puts the body into low-power mode. There is also the fact that by exercising you increase your appetite and also gravitate towards healthier foods. Whatever the reason, exercise does make you happier, and the more intense the exercise, the better. It does need to be the right kind of exercise – not toiling every day at low intensity like a labourer, but having brief, infrequent bursts of high-intensity activity.

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