Does Hiking Suppress Your Appetite?

Hiking Health

I must own up here and say I have an obsessive personality. The people who say you can’t put more than 100% into an endeavour have never met me. Thankfully this obsession isn’t aimed at illegal stimulants or gambling, but rather at food and exercise, and has always been my way. I only ever put on weight when these two counter-balancing obsessions get out of sync.

Over time I have learned to recognise the signals my body sends and do what is necessary to maintain my fitness level, and to a lesser degree my weight at a point with which I am happy. At some stage over the past few years I came to the realisation I lose appetite when I exercise so rather than stuffing my face at the end of the day when I get home from work, I walk up my local mountain and the hunger is gone.

Is this just me or does exercise supress hunger in everyone? And what does this mean for me as a hiker?

Several studies completed in recent years have confirmed there is a correlation between exercise and appetite with cardiovascular exercise, more so than resistance exercise such as weight lifting, being shown to alter the release of two key hormones, ghrelin which stimulates appetite, and peptide that suppresses appetite (see the links below).

What does this mean in practice?

While the science behind the effect doesn’t concern me too much, in practice this has a big impact for me particularly on very long or multi day hikes. Here is a practical example of the impact that appetite suppression has on me. You may not be affected in the same way but it’s worth considering for those longer hikes.

In December 2016, I undertook a one-day, 53 km walk to Mt Bimberi, in the Bimberi Wilderness near Canberra. I did this walk for several reasons however the main aim was to determine my capability to inform my planning of a series of long distance hikes I’m scheduling over the next seven years. My fitness level means I have no problem doing such distances and can back long days up over multiple days. I quite enjoy long distances as they provide me with a challenge.

On this trip, I was powering along quite well for the first 6.5 hours however, about half way up Mt Bimberi I just ran out of steam. This hit me in an almost instantaneous manner and it was like someone had poured concrete into my hiking shoes. I was struggling to move beyond a very slow walking pace. And then it occurred to me that while I had eaten a high calorie breakfast just prior to the start of the walk, I hadn’t eaten that much since – I had literally run out of fuel.

I hadn’t felt like eating but this was a mistake on my part. I took a short break and forced down some high calorie snacks even though I didn’t feel hungry and soon my energy returned. I made sure I ate again soon after, and once again when I reached the summit when I had my lunch and a good rest. Throughout the return trip I ate something at least every hour. Lesson learnt.

By the end of this day I had expended nearly 8,500 calories according to my Fitbit and I had lost 2.7 kg in weight. This weight loss was not fluid given the amount of water I drank – I always monitor my water intake very carefully.

On any normal day 8,500 calories is way past my normal calorie intake, more than double. On a day when I’m doing 15 hours of strenuous hiking there is absolutely no way I can replace the calories as I have no appetite and really don’t feel like eating even though I know should. Now I know Elvis Presley was supposed to be consuming nearly 10,000 calories a day prior to his death but I feel sick if I try to eat even half that amount and that’s from someone who loves food.

It is not unusual for me to lose 7-8 kg of weight over a two-week hike. If you read any number of blogs from males who have done the American long trails (e.g. Pacific Crest Trail) this is not uncommon with many of them looking like scarecrows by the time they have finished their hikes. Unfortunately for women your metabolism operates differently so Gill on the same two week hike may be lucky to lose 1-2 kg of body weight even with a much lower calorie intake.

The moral of this story?

While I don’t really monitor my food intake in my day to day life when I do very long days or multi day/week hikes, I must consciously monitor my food intake and ensure I eat high calorie snack foods every hour whether I want to or not. If I don’t, I run the risk of not being able to complete my hike.  Definitely a first world problem!

References

Broom et al. The influence of resistance and aerobic exercise on hunger, circulating levels of acylated ghrelin and peptide YY in healthy malesAJP Regulatory Integrative and Comparative Physiology, 2008; DOI: 10.1152/ajpregu.90706.2008 http://ajpregu.physiology.org/content/296/1/R29

https://www.sciencedaily.com/releases/2008/12/081211081446.htm

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