How long can you be in an energy deficit?
A recent study that followed a pro cyclist at the Tour de France Femmes avec Zwift showed that some cyclists can be in a deficit for more than a week while racing at the highest level. This cyclist’s average daily energy intake was around 5,200 kcal while her expenditure was around 7,600 kcal. Over the 8 days of racing, she stayed in a 2,400 kcal deficit, which resulted in her losing 2,2 kg of body weight. Despite losing weight, her performance remained unaffected. You can read more about the research and her diet at the Tour in our previous article.
The question is how long would she be able to sustain this level of performance while in a deficit. Renee McGregor, a sports dietitian specialising in relative energy deficiency in sports (RED-S), answered this in an interview:
“In the initial stages, you may not see any negative effects on performance per se. However, energy deficit becomes problematic in the longer term. Most people are fine for roughly three weeks – but after that, being in an energy deficit can lead to a rapid decrease in performance. Cyclists come unstuck because they don’t appreciate that their behaviour six months or a year ago is the reason why they are not able to maintain performance today.”
Reduced cycling performance
Some studies suggest that performance may be negatively impacted a lot sooner than after 3 weeks, depending on how big the deficit is and how hard you ride. A recent paper looked at exactly this. The researchers recruited 12 female triathletes who went through 14 days of normal eating followed by 14 days of eating only 50% of their energy needs. During both periods, they kept up their intense training schedule and underwent testing to assess their performance. During the period with insufficient calories, athletes lost, an average, 4% of their body weight and half of that weight was muscle. How did this affect their performance?
“The 14 days of insufficient food intake reduced their performance by 7,7% in a 20-minute time trial on a bike, which is quite significant. And during a more intense short-term test, their performance slid by as much as 18%. So, there is no doubt that this practice greatly impairs one’s performance as an athlete, even over shorter periods of time,” said Jan Sommer Jeppesen, a lead author of the study.
Refeeding over 3 days isn’t enough
The same study looked at what happens when you give athletes time to replenish their energy reserves. After those 14 days of low energy availability, they included a 3-day refeed where the triathletes could eat as much as they wanted. Did this help them improve their cycling performance?
“We had expected that the three days of enough food would restore their performance – and maybe even improve it – but there was absolutely no effect. Their performance was just as degraded as prior to the three days. This tells us that the negative effects cannot be reversed by quickly replenishing energy stores, which is a strategy used by many athletes,” commented Jeppesen.
Research like this shows that an energy deficit can be a double-edged sword. It needs to be used with careful planning behind it. Unfortunately, the pressure in pro cycling is often very high to be as light as possible to improve your power-to-weight ratio and be better at climbing. That’s why many cyclists don’t even consider going the other way.
Jonas Abrahamsen showed how the opposite can also work
Maybe it doesn’t have to be all about energy deficits and trying to get lighter. Jonas Abrahamsen recently showed that intentionally gaining weight can actually be the way to become a better cyclist.
“When I first got a two-year contract, I was gambling to gain some weight. I got a lot of help from my team and I was going up going from 60 kg to around 80 kg, so that was a big difference. Before I was happy when I got over 900 watts peak, now I have like 1,500 watts,” Abrahamsen said in an interview.
Gaining weight is what allowed Jonas Abrahamsen to reach his full potential. In the 2024 Tour de France, he led several breakaways and held the polka dot climber’s jersey for 10 stages as well as the green sprinter’s jersey for 3 stages and received the Combativity Award in 2 separate stages.
“On my passport, I am 177 cm, and after I started to eat, I got to 183 cm. I got more muscle and I also got taller,” he said. He also added that he got sick less often and it was easier to recover from hard rides.
It’s a great example of how much restrictive eating can hold back a talented cyclist. And this lesson is not necessarily only just for the pros. There are many amateur and club cyclists, especially in the youth categories, and particularly women, who are too focused on getting light at the expense of their health and longevity in the sport. We will take a look at why women are particularly vulnerable in the next part of the series.
