Is a keto diet effective for strength training?

Ketogenic diets have gained popularity in recent years among athletes. While these diets are just as effective for weight loss as any other diet that causes a calorie deficit, the evidence for a real sporting advantage over other diets is very mixed and it seems only in steady-state endurance sport that they may have some role. But what about in the gym? Is keto a viable option to both shred and bulk up at the same time? That’s what I explore in this podcast by looking at the findings of a recent review paper on this very topic.

Links referred to in the podcast

• Review of keto diet and effects on resistance training https://pubmed.ncbi.nlm.nih.gov/34578961

Episode transcript
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Transcript

Ketogenic diets have gained popularity in recent years among athletes. While these diets are just as effective for weight loss as any other diet that causes a calorie deficit, the evidence for a real sporting advantage over other diets is very mixed and it seems only in steady-state endurance sport that they may have some role. But what about in the gym? Is keto a viable option to both shred and bulk up at the same time? That’s what I explore in this podcast by looking at the findings of a recent review paper on this very topic.

Keto is the theme of today’s podcast, so let’s start off by talking about what defines a keto diet. Here, you are talking about limiting carbohydrate intake to less than 50 grams per day. And even lower if you can get it there. So that means for a normal diet that isn’t low calorie, it will be less than 10 percent of the total energy coming from carbohydrates. The remaining macronutrients come from fat – up to 80 percent of energy and then of course protein.

The idea behind going so low with carbohydrates is to increase ketosis. Ketones are what our body can use as a fuel source when carbohydrate is in short supply. We make ketones from fat. You have ketones in your blood right now, but when you are in ketosis from going on a keto diet, you have more of them.

It is promoted ad nauseam by those promoting keto diets that being in ketosis means you’re burning more fat. Just no – you’re being hoodwinked. Let me explain why. Yes, you’re burning more fat, BUT get the image out of your head that it is all coming from your body fat stores. It isn’t. The extra fat burning seen on a keto diet is majorly augmented from…..all that extra fat you are eating in place of carbohydrates. In the end, it is the calorie deficit caused by following a restrictive diet that results in weight loss, not any magical body fat burning ability of ketosis.

Keto diets saw a surge of popularity some years back with all sorts of promises of enhanced athletic ability and with plenty of champions on social media singing its praises. Firstly, in defence of keto diets, if a keto diet helps you lose weight and that then improves your power-to-weight ratio, then sports performance benefits could follow. But any diet can do that for you. The claims about keto were more to do with sparing glycogen stores and being able to better use fat as a fuel source in sport. Keto will do this, but there is enough research in to now show that the cost of this is reducing peak power output. And while you certainly can see evidence of metabolic changes in favour of fat adaptation when following keto, to paraphrase the doyen of sports nutrition, Professor Louise Burke, they don’t give Olympic medals for having optimised metabolic enzymes.

When oxygen is in short supply as during higher intensity activity, you make more ATP (which is the energy currency of the body), out of carbohydrate than fat per unit of oxygen. When you need to put the power down for a surge or hill climb, it is carbohydrates that are king, so this is the downside on performance of a ketogenic diet. In fact, a recent systematic review of 10 RCTs found no superior benefit of a ketogenic diet on VO2max, time to exhaustion, heart rate max or perceived exertion.

For long endurance steady-state activity however lower-carbohydrate diets may be beneficial, and why such diets are popular in the ultra-endurance world, but you will struggle to find much of a groundswell of support for them in most sports especially on competition day.

So, there can be a place for keto as part of diet cycling in training especially for endurance athletes and maybe even for weight loss, but you won’t find many podium athletes who got there from doing keto day in and day out.

But what if you want to get strong and build muscle? Keto diets are growing in popularity among strength-trained individuals, and indeed these diets have been proposed as an option for some athletes. These include people participating in weight-category sports or in events where a high ratio of muscle strength relative to body mass is required for success (such as high jumpers), as well as bodybuilders wanting to drop body fat without losing muscle mass during the ‘cutting phase’ of their training.

However, controversy exists as to the actual effects of a keto diet on body composition and performance in strength-trained individuals. And there is evidence they could even be detrimental. So, let’s take a look at what a recent review on this very topic had to say.

This was a narrative review of 9 randomised controlled trials. It looked at the evidence on the effects of keto diets that were followed for a minimum of 2 weeks on body composition and measures of muscle function including strength and power output. And I’ll link to the review in the show notes. https://pubmed.ncbi.nlm.nih.gov/34578961

Not all the trials in the review were the same. Seven of the 9 trials matched energy intakes between the keto and control diet groups. The other two trials let participants eat to their own preferences.

Looking at weight loss and body fat loss, 6 of the trials found the keto diet to be better. In the other 3 trials, weight loss was similar between groups. This isn’t really a surprising finding, as short-term, keto can result in greater weight loss and this is well known, but long term because of the ability to stick to it and stay in ketosis, weight loss differences taper out.

But things start to look different when you focus on fat-free mass changes. Fat-free mass includes not only your muscles, but also your organs, glycogen stores and how much water is in your body. In 5 of the trials, the keto group lost more of their fat-free mass. Here is why: when you go on a keto diet, you deplete your glycogen stores and because each gram of glycogen is bound to several grams of water, that can mean easily losing 1 to 2 kilograms of fat-free mass. That is all smoke and mirrors because the day will come I promise you that you will eat carbohydrates again and you simply gain that weight back again as you replenish your glycogen stores.

So, taking that all into account, keto really had nothing that special to offer for weight loss – and by weight loss here I mean what people really mean by it when they talk about losing weight: and that’s body fat loss. For weight-category sports, short-term keto could be a better option but has to be balanced against going into competition glycogen depleted and remember, that’s the fuel your body used for getting peak power output.

So, what about the meat of the review? How does keto fare when you look at strength and power? Seven of the 9 studies looked at these effects in strength-trained athletes. In three trials, the keto group had less improvements than the control group. In the other 4 RCTs, both groups had similar improvements in strength and power. So that’s not glowing news for keto.

Why could a keto diet be worse for muscle growth and power? The authors had a few ideas.

• By cutting back on carbs, keto diets reduce insulin levels. Insulin is not the devil you may hear about in the keto world – it has important roles to play in amino acid update into cells and it also increases protein synthesis. So, less insulin could mean reducing muscle protein synthesis
• Keto diets might also interfere with cellular signalling which can inhibit muscle-building anabolic pathways.
• And finally, because keto diets can suppress appetite, thereby reducing energy intake, they may make it harder to build and maintain muscle because not enough fuel is taken on.

So, let’s wrap all this up. For strength and power athletes, keto diets can help with weight and fat loss. Which for these athletes that could improve their power-to-weight ratio. However, when it comes to the muscle gainz which is the competing priority resistance training athletes want to focus on, keto appears to have less to offer and could even be inferior to a more balanced diet for building muscle mass and strength. Combine that with underwhelming evidence showing there isn’t much of an overall sports advantage to, and more likely a detriment, in endurance athletes, then it is no wonder that you are probably hearing less about this diet in the sporting world these days.

So that’s it for today’s show. You can find the show notes either in the app you’re listening to this podcast on if it supports it, or else head over to my webpage www.thinkingnutrition.com.au and click on the podcast section to find this episode to read the show notes.

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I’m Tim Crowe and you’ve been listening to Thinking Nutrition.