Us climbers can be pretty obsessed with numbers. Our thoughts are often occupied with grades, how much weight we add to hangs, how many seconds we hang for, the number of moves in our circuits and of course… how much we weigh. Most climbers are aware of their weight and sometimes this can motivate an unhealthy, or even dangerous, relationship with food. With this in mind, there’s been some talk of implementing BMI (Body Mass Index) cut-offs for competition climbers, as a way to keep climbers healthy and eating disorder free. As a sports dietitian who works with athletes with eating disorders, implementation of measures to prevent such disorders is always front-of-mind. However, I can’t help but question if BMI is the right tool for the job, and whether there are better red flags to look for?

BMI is calculated by dividing your weight (in kilograms) by your height (in metres squared). The measure was created in the 1800s by Adolphe Quetelet, a Belgian mathematician who was interested in defining the average man. In the late 1800s, BMI was adapted to estimate lifespans and since then it has become a diagnostic measure that tells adults whether they are 'underweight' (BMI under 18.5kg/m2), a 'healthy' weight (BMI 18.5-24.9kg/m2), 'overweight' (BMI 25-29.9kg/m2), or 'obese' (BMI over 30kg/m2).

Health researchers have found that BMI is a good indicator for the health and lifespan of adults. It is used to assess for risk of chronic diseases (such as diabetes, heart disease and cancers) and to identify people at risk of developing an eating disorder.

It is important to understand that BMI is used to predict health outcomes and lifespan of a group who have the same BMI, not for an individual. For example, researchers have shown that a group of people with BMIs in the 30’s have more chance of dying younger and developing a serious illness, on average, than a group whose BMI is in the 20’s. Furthermore, the World Health Organisation states that “to achieve optimum health, the median body mass index for an adult population should be in the range of 21 to 23 kg/m2, while the goal for individuals should be to maintain body mass index in the range of 18.5 to 24.9 kg/m2”.

So, BMI works well enough when looking at groups and is applicable to most of the population as a predicter of health, but it doesn’t take into account body composition or body shape, and this is where its application is limited. Two people could be the same height and weight, but the one who carries fat around their middle will have more visceral fat and therefore will be at a higher risk of disease than the other. Similarly, when you start applying BMI to individuals in sport, it can get complicated because it doesn’t account for lean muscle or frame size.

What does this mean for us climbers? The motivator for monitoring comp climbers’ weights is to identify eating disorders and prevent injury and illness related to being underweight and malnourished. Research tells us that maintaining a low BMI over time can mean we are not getting all the nutrition we need to keep our bodies working well. This means we can’t recover properly and our risk of developing and overuse injury increases. It can also change our immune function and can impact our overall health. Low BMI can also result in lower bone mineral density, and as climbing involves less weight bearing than a sport like running, climbers have been found to be at a higher risk of this anyway. When we look at young climbing athletes, the combination of high training load and low BMI can increase the likelihood of stress fractures and bone deformities which will impact their long-term health and their ability to train hard over a longer period of time.

So, should BMI cut-offs be applied to competition climbing?

As a cut-off to exclude an athlete from competition, my belief based on the current research is no. But as a screening tool to check-in with an athlete and flag them for further investigation, yes.

When we look at a body weight sport like climbing, low BMI can indeed indicate malnutrition. However, elite level climbing is likely to include climbers who are outliers; taller and skinnier or smaller framed and lighter than the average population.

It is essential that an athlete’s nutrition is meeting their needs to be able to cope with training loads and comp stress and BMI is certainly a way of identifying if a climber is underweight and potentially malnourished.

BMI is a good tool but not the one measure to rule them all.

It is a great red flag for a coach and sport dietitian to assess food intake, training load and energy intake, bone density and hormone levels (menstrual cycle for women), immune function (is the athlete getting sick a lot?) and to look at body image and attitudes toward food. If we manage to check-in with our athletes sooner, they will have longer, stronger climbing careers. And who doesn’t want that?

Amanda Watts is an Australian Accredited Nutritionist and SDA Sports Dietitian. Amanda founded Thrive Nutrition & Dietetics because she is passionate about connecting people to what matters – their health, their food and each other. When she’s not working as a dietitian, Amanda can be found climbing in the Blue Mountains, training or traveling the world to climb in new places. Over her 23 year climbing career, she has represented Australia in World Cup sport climbing, consistently been on the podium at bouldering nationals and has performed at an elite level across sport and trad climbing.

If you have any questions for her, send her an email or contact her on Instagram on @a.mandawatts or @thrive_nutritiondietetics