How Unhealthy Is Running?

[TLDR: Let’s look at some of the science around the health benefits (or otherwise) of long-distance running. Like everything else on this blog, these are not specific recommendations but rather my referenced views on the overall literature. If you're interested in the question of whether or not long-distance running is healthy for you, please book a free consulation.]

Recently I made a video on the dangers of long-distance running. Runners were in the comments straight away. They were not pleased.

Do the runners have a point? Is running really unhealthy? Or am I overstating the case?

First of all, let’s clarify our terms here. What I mean when I’m talking about running is long-distance running. Let’s call it marathon training, though ultra-marathons like the Comrades in South Africa would also fall in this category. I explicitly don’t mean sprinting or even shorter distance running - training to run a race of less than 8 kilometres. Running short distances is a completely different topic.

Is it even true that people who run marathons are at a higher risk of heart disease and/or all-cause mortality?

Looking at the literature it’s extremely hard to answer this question. We do know that some people even some young people will die during the course of running and training for long-distance runs. But would those same people (or even a greater number of people) have died doing some other activity? Would they have died doing no activity at all?

Some of the studies that have begun to look into the dangers of long-term running include the following:

1. https://doi.org/10.1159/000537993
2. https://doi.org/10.1177/1941738110373066
3. Why Do Healthy People Die Running Marathons? (Forbes)

To sum up the conclusions from these studies, yes it appears that marathon runners may have a higher risk of dying from heart disease compared with some populations, but they also have a lower risk of heart disease than other populations. If we compare people who run marathons with people who do nothing but sit on the couch all day, the risk seems to be lower.

So what’s really going on here?

From my perspective as an anthropologist, different biological systems are adapted for different physical activities. The one activity that no creature with a brain is designed to do is to sit in one place all day. Unfortunately "sitting in place" describes a sizeable chunk of the population. Hence there are studies which show that sitting is as bad as smoking. So based on this evidence marathon running seems to be healthier than sitting on a couch all day.

But is this a false choice? Are the only two options sitting in front of a screen all day or running 100 kilometres+ per week?

We know that long distance training - like all training - leads to certain physical adaptations. In the case of long-distance running, those adaptations are generally thought to be beneficial - lowering of blood pressure, an increase in one’s heart rate variability (HRV) score, etc. Some of those adaptations, particularly the enlarging of the heart, might be dangerous. But that happens fairly rarely.

One particular adaptation that happens in people who train zone 2 cardio chronically (I would use the word overtrain) has to do with the muscle. At a general level we tend to talk about two types of fibers in muscle - slow twitch or type 1 and fast twitch or type 2. In order to run a marathon one needs to have a lot of type 1 muscle fiber and very little of the type 2 or fast twitch muscle fiber. From my perspective as someone who’s interested in health and heart disease that’s already a problem. One of the things that we need our muscle for especially as we get older is to be able to store glucose in the form of glycogen. Type 2 muscle fibers are better than this than type 1 fibers.

Secondly, because long distance running is not a particularly glycolytic exercise - in other words it’s mostly fat that runners are using to “fuel” their run - runners tend to have molecules of fat actually in the muscle tissue itself. These are known as intramyocellular lipids (IMCLs). Studies including this one show an association between IMCLs and hyper-insulinemia, which is what I’m really concerned about. High insulin levels are associated with (and high sugar levels contribute causally to) type 2 diabetes, cancer, Alzheimer’s disease and other forms of dementia. These “plagues of prosperity” are what we really need to be concerned about at every level when optimising for health and longevity.

In other words, the physiological adaptations to long-distance running are not ideal for those concerned about health and longevity. When you add to that a less-than ideal diet, a diet based on excess carbohydrate consumption, you are compounding the risk of these side-effects. And the specific way in which a high-carb diet is done for many runners compounds those negative side effects even more. When you take in a bolus of carbohydrates your blood sugar will spike. And when you exercise your blood sugar will also spike. If you are constantly taking an unnecessarily high dose of carbohydrates while exercising you’re adding a blood sugar spike on top of a blood sugar spike. Add to that the fact that the runner's body likes to store energy in the form of fat, and you have the possibility that a lot of those carbs are being turned into fat and stored either in the muscle or (worse) in or near the organs, including the heart. 

Do we have the data to confirm that people who train in this way have worse results? No we don’t. But does that mean it’s safe to do so? No it doesn’t. Absence of evidence is not evidence of absence. The processes I'm describing are well-documented at the level of human physiology. 

So the question I would like to ask anyone who engages in long-distance running is the following: why do you want to consume so many carbohydrates? We have very good data showing that the same individuals performed exactly the same whether they were on low carb or high carb diets. This is data from "The Effects of Carbohydrate versus Fat Restriction on Lipid Profiles in Highly Trained, Recreational Distance Runners: A Randomized, Cross-Over Trial” . And that conclusion has been replicated in similar trials from other research teams.

If there is a clear down-side (you’re leaning your physiology into the diabetogenic pathway that long-distance running will induce in any case) and no clear upside (you can perform as well on low carb diets after an adaptation phase), what’s the point of the high-carb diet for training?

At a minimum, what I'd be doing if I were a long-distance runner is to ditch the carbs. The possible exception would be race day, when a minimum level of carbohydrate (Prof. Noakes says about 10g per hour) may be necessary to ensure optimal performance. Commenters who claim they could never perform on such a low level of carbohydrate consumption may indeed be right, but that's because they haven't trained in a low-carb state. After an adaptation period, we find that the carbs were never necessary in the first place. 

At the end of the day, I'm not telling anybody what to do. Exercise, or at least movement, is important. The kind of exercise you do will depend on your strengths, your interests and what you're optimising for. For those optimising for longevity (and that's not everyone) I think there is a strong case to be made against long-distance running. For those who want to do it anyway, I would humbly suggest we find ways to help you do it while minimising the damage. 

For those who do want to focus on longevity first and then ask the question "what movement pattern would most benefit me from a health and longevity point of view?" I think there are a number of possible answers. There's a good case to be made for racquet sports given the observational data that those who play racquet sports tend to have long and healthy lives. There might be a case for something like sprinting, given what we've said about type 2 muscle fibre. There's definitely a case for walking as the most ancestrally appropriate movement pattern. 

But to my mind none of these are a clear winner and none of them should be seen as exclusionary to any other one. One could sprint a little, play a little tennis and walk regularly. And in terms of the data I can't say with any confidence whether these three or something else would work, either for an individual or for a given population.

There may not be one right way to exercise, but it seems clear to me that there are wrong ways. Long distance running would be high on that list given what we know about the physiological adaptations and the popularity of carbohydrate consumption within the sport.