Lockdown nutrition: eat fat to stay lean?

With training options curtailed for many, Sports Performance Bulletin looks at some recent research suggesting a higher-fat diet could provide weight management benefits during the current coronavirus lockdown

According to the latest statistics, there are now over 1 billion people worldwide in various forms of lockdown due to coronavirus. This means that the opportunities to train for endurance athletes in these areas are at best reduced or at worst, severely curtailed. With that in mind, many athletes will be wondering about the implications for their fitness going forward.

The good news is that research shows a reduced training volume – or even the complete cessation of training - for a week or two has little impact on long-term fitness levels, and is generally not considered too disruptive providing that the previous training adaptations have been achieved over a period of at least twelve weeks or more⁽¹⁾. Indeed, a short period of rest or greatly reduced training volume allows muscle to become properly rested, which can actually lead to performance gains. This is the rationale behind the process of tapering in the run up to a race or important event.

Even better, research has shown that a significantly reduced volume of higher intensity exercise – for example high-intensity interval training - can be remarkably effective at producing fitness (and halting its decline). For example, a 2006 study demonstrated that 2.5 hours of sprint interval training produced similar biochemical changes in muscles to 10.5 hours of endurance training and similar endurance performance benefits⁽²⁾.

The longer-term slide

While tapering for a race, or taking it easy while you’re on a 2-week vacation or work project is unlikely to significantly dent your fitness (and may actually allow you to become properly rested!), the landscape looks different for longer periods of time – for example during a lockdown. Here in the UK, our 3-week lockdown is about to be extended for another three weeks, with no guarantee that it will be lifted in May either. Once the timescale of reduced activity extends into months, there are negative consequences. While fitness levels can be largely maintained by focusing on high-intensity training sessions, training at home will inevitably lead to reduced training volumes – either because of sheer boredom, or because the restrictions on movement make it practically impossible to get out and train.

Once training volumes drop, total energy expenditure levels will drop, which means that the equation between energy in vs. energy out shifts to the left, unless energy (calorie) intake is reduced accordingly. If calorie intake is not reduced, the inevitable consequence is an increase in body fat. A small increase of a percent or two in the level of body fat is not a major problem; most athletes will find that this reduces back down once normal training is resumed. However, a larger increase in body fat is more impactful. Not only will it seriously reduce your power-to-weight ratio (see this article for an-depth discussion on power-to-weight), it may require many months of training to reduce your body-fat level back down to what it was, and for you to become competitive again.

The research linking lower training volumes with higher levels of body fat (adiposity) is solid. For example, in one study, scientists found that a 1-year prescription of moderate to vigorous exercise for 300 minutes per week resulted in significantly lower total fat and other adiposity measures than the same exercise prescription for 150 minutes per week⁽³⁾. Studies also show that for long-term weight management, those who exercise for more than 200 minutes per week are likely to maintain lower levels of body fat than those who exercise between 150-200 minutes per week, with those who exercise less than 150 minutes per week achieving even poorer outcomes^(4,5).

An alternative strategy?

It’s frustrating enough not being able to train the way you’d like to, without adding in another frustration of not being able to eat freely because of the need to calorie restrict! But could there be another nutritional strategy in the low-volume training-restricted times? One possible strategy that might be worth considering is the use of a high-fat, low carbohydrate diet. In recent years, a growing body of recent research has emerged suggests that a diet embodying this approach and eschewing the intake particularly of refined carbohydrate can help promote weight loss and improved markers of cardiovascular health in those who are overweight.

However, while there’s good evidence for the use of this kind of diet for those with health conditions related to obesity, as a nutritional tool for endurance athletes, the benefits are far less clear. As we have previously discussed at length in Sports Performance Bulletin, while this high-fat, low-carbohydrate approach (often referred to as ‘keto-eating – see this article) can certainly help increase fat oxidation, there’s very little evidence that it leads to enhanced performance – indeed, performance at very high intensity may actually be diminished. One reason for this is that while fat oxidation and body fat loss is enhanced, carbohydrate oxidation may become less efficient, which could impede performance during flat out exercise. However, a study on older runners from 2018 suggests that a short to medium-term application of this approach might produce performance benefits by maintaining performance while keeping weight down – without the need for calorie restriction⁽⁶⁾.

In this study, US researchers examined the effects of a 3-week high-fat, low carbohydrate diet on markers of endurance performance in a group of middle-aged, recreationally competitive male runners. This diet restricted the amount of carbohydrate the runners consumed each day to a maximum of 50 grams. However, the runners were free to consume as much high-fat food as they wished – ie it was NOT calorie restricted. Overall, the high-fat foods contributed around 70% of the runners’ total calorie intake. Before and after the 3-week diet intervention, the runners’ levels of body fat were measured along with their physiological responses when running at race pace. In addition, all the subjects completed a 5km time trial road run as fast as they could and the results were then compared.

After three weeks on the low-carbohydrate, high-fat diet, the runners didn’t gain any weight – in fact, they LOST 2.5kgs of body fat on average, which is a significant amount for such a relatively short intervention. Also, regardless of the pace at which they ran, all of the runners increased the amount of fat burned for energy, while carbohydrate oxidation was reduced. In terms of their 5km time trial performances however, there were no significant differences between the ‘before’ and ‘after’ times.

Implications

This was yet another study to show that a low-carbohydrate, high fat can result in significant fat loss. The fact that it also occurred in competitive runners who weren’t carrying large excesses to begin with, and who were allowed to eat freely in terms of calorie intake is intriguing, especially as the fat losses were quite large and occurred in a short time frame. Commenting on the (broadly unchanged) performances following the diet, the researchers speculated that while the low-carb, high-fat diet had reduced carbohydrate oxidation during exercise (which would normally reduce performance), this loss was offset by the reduction in body fat (a better power-to-weight ratio) and increased fat burning.

In normal times of course, this would leave open the possibility of ‘the best of both worlds’ approach – three weeks on a low-carb, high-fat diet to reduce body fat, followed by a couple of days a high-carb diet in preparation for a race or competition shortly afterwards. This would enable runners to both shed body fat and ensure carbohydrate metabolism is fully optimised again, allowing maximum race intensity. However, it could also prove a useful tool for athletes in lockdown – as a means to control or even reduce body fat levels while training volumes are restricted.

Don’t forget too, there are other strategies that seem to help weight management, and which don’t involve traditional dieting/calorie restriction. One of these, which we’ve also explored at length in Sports Performance Bulletin is the use of time restricted feeding (see this article for an in-depth explanation). To find out more about these strategies and how to implement them practically on a day-to-day basis, readers are directed to the article links below.

Finally though, it’s worth bearing in mind that even if your training is severely curtailed, you shouldn’t be too disheartened. That’s because everyone else in your region will be in the same boat as you, so you won’t necessarily be at a relative disadvantage. Also, for those athletes who have been in intense training, a long layoff might bring new performance benefits by allowing some ‘deep’ rest for the muscles. Having said that, athletes who can keep a reasonable base level of fitness and maintain a good power-to-weight ratio will be the winners when the lockdown is finally lifted!

References

1. Annals N. Y. Acad. Sci. 1977; 301:431-439
2. Sports Performance Bulletin 2006. 223; p4-6
3. JAMA Oncol. 2015 Sep;1(6):766-76
4. JAMA. 1999 Oct 27; 282(16):1554-60
5. JAMA. 2003 Sep 10; 290(10):1323-30
6. Med Sci Sports Exerc. 2018 Mar;50(3):570-579