Weight management: are you heading for trouble?

New research suggests that calorie restriction as part of a weight management plan can rapidly produce unforeseen and negative consequences. Andrew Sheaff explains

To be successful in endurance sport, athletes need to move their body through space for extended periods of time. To do so, athletes need to accomplish two tasks. Firstly, endurance athletes need to be capable of creating as much power as possible for the entire race distance. They need to be able to create a reasonably high power output, and they need to have the fitness to sustain that output.

Building this capacity to sustain moderately high levels of power requires a prolonged period of challenging training paired with adequate recovery, and requires a lot of energy to fuel the necessary training. In addition, it requires enough energy to rebuild during the recovery process so that the athlete can come back stronger than ever.

Secondly, endurance athletes need to be as light as possible; if an athlete can produce the same power output at a lighter weight, they will go faster (see this article on power-to-weight ratio). As a result, many athletes attempt to reduce their weight, or maintain a body weight that is artificially low.

Energy availability

The only way to accomplish these goals is to reduce energy availability. Energy availability is the energy left over after subtracting the energy required to perform sporting activities from total energy (calorie) intake. This is a key metric because it takes into account both the dietary intake and the training energy expenditures. Even if an athlete has a very high energy intake, they can run into problems with energy availability if their training volumes are extremely high. Likewise, another athlete might have a much lower energy intake, but due to very low training volumes, they could have adequate energy availability. Lowered energy availability can arise from excessively high training volumes or from low dietary intakes, or from both (in this case rapidly!).

Conflict of needs

Problems arise when athletes are training hard to improve their performance and keeping energy availability low to reduce their weight. On one hand, hard training requires a high energy availability to allow for the work to be completed as well as successful adaptation. On the other, a body mass reduction requires low energy availability. Creating the optimal environment for one goal compromises the ability to accomplish the other. If an athlete attempts to reduce body mass to improve performance, they run the risk of compromising their training, thus decreasing their performance.

In the quest for optimum or lower body mass, many athletes mistakenly compromised their training and their performance by reducing their energy availability too far. While this makes sense conceptually, there isn’t much experimental evidence in the scientific literature as to the exact short-term changes that actually happen when athletes begin training with low energy availability. To what extent do performance measures change? To what extent do measures of overall health change? To what extent do measures of well-being change? While it’s generally understood that low energy availability has generally negative impact on these measures, it’s important to determine how quickly these negative outcomes arise, and the relationship between this process and magnitude of energy availability reduction.

New research

A very recent study has examined the impact of reduced energy availability in male endurance athletes⁽¹⁾. The athletes performed four different stages in this study:

1. A baseline stage where training and energy intake was monitored without any intervention
2. A separate 14-day stage, with a 25% reduction in energy availability.
3. A second separate 14-day stage, with a 50% reduction in energy availability.
4. A third separate 14-day stage, with a 75% reduction in energy availability.

The subjects performed each of these stages in a randomized order, with one month of normal energy availability separating each stage (to ensure that the previous stage had no impact on the current stage). The results were clear and quite alarming (see figure 1):

• Power output during a cycling endurance test was compromised.
• Just as importantly, relative power output was also compromised, implying that the performance benefits of any weight loss were more than offset by the losses in power output.
• Losses in explosive power output as measured by jumping and the ability the ability to produce lactate were demonstrated as well.
• As energy availability decreased, so too did anaerobic threshold (athletes started produced fatiguing lactate at lower intensities than normal).
• Beyond immediate performance measures, testosterone levels decreased as energy availability decreased, and the level of cognitive restriction increased with decreasing energy availability.
• Mental well-being suffered throughout the intervention, worsening with decreasing energy availability.

So marked were these reduction that when performing the stage with a 75% reduction in energy availability, none of subjects could even complete all 14 days!

Figure 1: Negative outcomes with energy availability reduction

Left: countermovement jump ability, relative power output and absolute power output declined drastically as energy availability reduced. Center: body fat % fell as energy availability reduced but this also resulted in a large drop in circulating testosterone (TQ - a powerful recovery hormone). Right: As energy availability reduced, well being (WB) fell while measures of dietary restraint (TFEQ – high levels are considered to cause more emotional distress) rose.

All the outcome measures, tended to get worse as energy availability decreased, accelerating as energy availability became was lowered. This indicates that the negative impact of low energy availability is magnified as energy availability is lowered. While the weight loss might come faster at lower energy availability, the consequences become much more extreme. Interestingly, the relationship between energy availability and hormonal changes was much weaker than the relationship between energy availability and well-being and performance. It appears that although performance and well-being are impacted during initial reductions in energy availability, it may take more stress to create larger problems in the underlying hormonal and physiological systems.

Practical advice for athletes

Clearly, prolonged and severe reductions in energy availability will have substantial and sustained impacts on performance and health. There are significant losses in measures of power, measures of well-being, as well as compromised hormonal function.  These changes all happened in a matter of weeks, not months. The key take home message is that it is very easy to get yourself in trouble in a small amount of time.

If weight loss is desired therefore, it’s a process that must be undertaken with this knowledge in mind. It is not a ‘more is better’ situation or a ‘faster is better’ situation. If you’re going to undertake any kind of weight loss intervention, be patient and be reasonable. Understand what a realistic amount of weight is to lose and give yourself the appropriate amount of time to do so. There’s no hard and fast rule on how quickly sustained weight loss can be achieved, but some research suggests around 1-2lbs (0.5-1.0kgs) per week is as much as you should aim for⁽²⁾. If you attempt to rush this process, you’re more likely to harm your performance than help it.

Likewise, it’s critical to monitor your progress during the intervention. Not only should you keep track of your physical performance, use a well-being questionnaire on a frequent basis to determine the non-performance impact of your weight loss strategy. The researchers suggest doing so every fortnight. If your performance or your well-being start to trend downward, it’s well worth considering a pause of the diet, or simply abandoning the strategy altogether. The impact of prolonged reduced energy availability is significant and severe. If choosing to reduce your body weight, be cautious and monitor well.

References

1. J Int Soc Sports Nutr. . 2022 May 25;19(1):179-195.
2. Am J Health Promot. 1996 Jul-Aug;10(6):471-98