Team-sport fitness: the keto route to lean and mean?

Can a keto diet help improve body composition and power-to-weight ratio? SPB looks at new evidence from soccer players

What separates elite soccer players from merely good amateurs? Technical skills, game intelligence, mindset, and fitness levels all play a part, but another defining characteristic is body composition. Studies show that elite players have very favorable body compositions (ie high levels of lean muscle mass and low levels of body fat), while lesser players invariably have poorer body compositions⁽¹⁾. This is important because an excess of body weight and body fat, and lower levels of lean muscle tissue is strongly correlated to detrimental effects upon soccer health and soccer-specific actions such as dribbling, ball control, speed and power⁽²⁾. For amateur soccer players wishing to improve performance therefore, optimizing body composition as far as is reasonably possible is a good strategy.

Routes to leanness

Following the correct training program and adopting a generally healthy lifestyle are important factors when trying to improve body composition. However, the overriding factor without doubt is good diet. Different nutritional approaches are typically used according to specific player’s characteristics, eating habits and different energy demands during competitive or non-competitive season⁽³⁾, and during competitive season, a relatively high-carbohydrate diet is usually recommended both on training match days in order to meet energy demands⁽⁴⁾. During the off-season however, when training ceases, amateur soccer players (and indeed other team sport athletes) often gain significant amounts of body weight and body fat. This often then leads to crash dieting using extreme calorie restriction – an approach that is known to be harmful both for health and athletic performance outcomes⁽⁵⁾.

The keto alternative

An alternative approach to the drastic energy restriction approaches is to follow a keto (ketogenic) diet. This is a nutritional strategy consisting of high fat, adequate protein and low carbohydrate intake but where which the amount of total available energy overall is adequate⁽⁶⁾. During a keto diet, the key is to keep carbohydrate intake very low – ie carbohydrates should contribute less than 5% of total daily energy intake or be kept under 30 grams per day.

The use of keto diets in sport is a fairly recent phenomenon and still an area of controversy, with studies showing conflicting results, especially when it comes to performance (see this article for an in-depth discussion). Some research has shown that keto diets can actually lead to worse performance, even when athletes switch back to a normal diet before competition^(7-9). This may occur because energy production pathways used during intense exercise become down-regulated after a period of low-carbohydrate intake. Meanwhile, other studies have found small positive effects or, at least, no detrimental effects^(10-14). More generally it seems to be that whether or not keto diets offer a benefit is likely to depend on sport type, with power and strength athletes most likely to see benefits while endurance athletes are least likely (and may even suffer poorer performance)⁽¹⁵⁾.

From a soccer perspective – a sport where there is a need for power, strength and agility AND endurance, there’s almost no data on the benefits or otherwise of keto diets. Given many non-elite soccer players might benefit from improved body composition, could a period of keto eating yield benefits such as an improved power-to-weight ratio, without harming soccer-specific performance? Research published by Italian scientists at the University of Padua has tried to answer that question in a new study published last month in the Journal of the International Society of Sports Nutrition⁽¹⁶⁾.

The research

In this study, 16 semi-professional male soccer players playing for a local team (A.S.D. Riviera Del Brenta, Venezia, category one), were recruited. To be eligible for this study, players had to meet the following criteria:

• No cardiovascular, respiratory, gastrointestinal, thyroid or any other metabolic diseases
• No recent dieting
• No adherence to special diets
• No use of nutritional supplements (except a daily multivitamin-mineral)
• No use of medication to control blood lipids or glucose
• No goal-keepers

During the study, all the players were asked to keep their normal and constant training schedule (consisting of eight hours of training per week). Before the start of the study, athletes were divided into the keto diet group and the ‘Western diet’ (control) group, which had to be followed for 30 days. Players in the keto group were provided nutritional counselling and resources to help ensure they were able to adhere to the keto diet.

Resources included food lists containing the food prohibited and permitted in ketogenic diet and electronic-suggested daily meal plans, meal recipes. The food lists encouraged the consumption of beef, veal, poultry, fish, raw and cooked vegetables without restriction, cold cuts such as dried beef, eggs and seasoned cheese (parmesan), fruits with the lowest glycemic index (blueberry, raspberry), raw nuts and seeds, ghee butter, plant oils and fats from avocado, coconut and olives – see figure 1.

The control group’s diet meanwhile (a good, healthy Western diet) was composed mainly of whole cereals (spelt, rye, oat) and pseudo-cereals (buckwheat, quinoa, amaranth), whole grain pasta, potatoes, meat, fish, vegetables, fruit, legumes, olive oil, milk and red wine (at most 1 glass per day). The Western diet was also composed to ensure a constant energy and macronutrient balance: protein 1.8 grams per kilo of bodyweight (30% of calories), 20–25% of calories from fats and 50–55% of calories from carbohydrates.

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Figure 1: Foods encouraged on the keto diet

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During a 3-day period before the start of the 30-day intervention and then again at the end of the intervention, the players’ measures of bodyweight and body composition (lean body mass and body fat %), resting energy expenditure (REE), muscle cross sectional area (CSA) and isometric muscle strength of quadriceps, counter movement jump performance (CMJ) and yoyo intermittent recovery test times were recorded. See figure 2 for a more detailed breakdown of measurement protocols.

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Figure 2: Before and after measurements

The testing procedure was performed over a 3-day period both before the intervention and then again at the end. Key is as follows: REE - resting energy expenditure; RER - respiratory exchange ratio; DXA - dual-energy X-ray absorptiometry (to measure body composition); CSA - cross sectional area; MCV - maximal voluntary isometric contraction; CMJ - counter movement jump; Yo-yo test - yo-yo intermittent recovery test at level 1.

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The findings

After the 30-day dietary intervention, the key findings were as follows:

• During the 30-day dietary intervention, carbohydrate intake was significantly lower and fat intake significantly higher in the keto diet (as intended). Importantly, protein and calorie intakes in both groups were very similar.
• Both groups lost weight during the diets (keto diet 1.55kgs; Western diet 0.92kgs), but there was a significantly higher decrease of body fat, surface adipose tissue and waist circumference (a good indicator of abdominal fat) in the keto group compared to the Western diet group (4.19cms drop in keto; -1.38cms drop in Western diet).
• Lean muscle tissue, quadriceps muscle cross sectional area (girth), maximal strength and resting energy expenditure did not significantly change in either group.
• The Yo-yo intermittent test performances improved significantly both groups without significant differences between the groups.
• The countermovement jump performance significantly improved in the keto group but not in the Western diet group.

In short, adopting a keto diet for 30 days enhanced body fat loss in the keto group without negatively impacting muscle mass (ie body composition was improved) or key measures of performance relating to soccer. Indeed, the fact that countermovement jump performance was enhanced only in the keto group is a good indicator that this group experienced meaningful improvements in power-to-weight ratio.

Practical implications

This is the first study to date that has investigated the effects of a keto diet on performance in team sports, such as soccer. The fact that these semi-professional soccer players underwent a significant reduction in body weight, body fat mass and waist circumference without any negative effects on strength, power and muscle mass is very encouraging. Unlike crash diet approaches, these results suggest that a limited period of keto eating can help improve body composition and power-to-weight ratio without losing hard-won muscle mass and strength!

Before all soccer players rush out and start following keto diets, there are however a couple of caveats to mention. Firstly, this intervention took place during a period of relatively light training and where no competitive matches were scheduled. Had training demands been higher, or had the players been required to play competitively during this period, their low carbohydrate intake may have worked against them. This suggests that the use of keto diets is best reserved for the off season rather than during the active season.

Secondly, it’s worth noting that even following the good healthy Western diet yielded some benefits in terms of weight loss. For athletes who struggle when trying to consume a very low-carbohydrate diet (and many do), this is encouraging. Simply improving the quality of an existing mixed diet, and radically cutting down on refined carbohydrates, processed foods and sugars is still likely to produce significant benefits.

Finally, while the keto diet proved particularly effective at dropping weight, athletes should not regard this as a ‘get out of jail card’ – ie a green light to gain weight freely each year at the start of the off season. That’s because research shows that frequent weight yo-yoing through diets followed by weight gain can end up leading to more and more permanent weight gains in the longer term^(17,18). A better strategy is to try and ensure your day-to-day diet is as good as it can be all year round! (See this article for guidance and tips).

References

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