Keto is the word of the month. Eating fat is definitely back with a vengeance.

So, is Keto the answer?

Though I have my own personal opinions about the sustainability and desirability of this diet, in my office, it always comes down to my clients’ goals, and current evidence.

Ketogenic diets are high fat diets that are extremely low in carbohydrate and only moderate in protein. Although this depends on the goals and the individual, generally the energy breakdown to achieve actual ketosis is >75% Fat, <10% Carb, ~ 15% Protein or less.  In practice, this translates to a lot of added fats like nuts, avocado and oils, lots of greens, a palm size portion of meat or fish, and maybe 4 raspberries per day, if you’re lucky.

 Why do Keto?keto_bowl

  1. Therapeutic diet for TBI and epilepsy
  2. Possible benefits for metabolic disorders ie. PCOS, obesity, Type 2 Diabetes
  3. Endurance training

Is it safe?

The short-term effects of Keto are mostly just inconvenient. Most will experience fatigue, weakness, headaches, cravings, possible hydration and electrolyte disturbances, and poor athletic performance. But, in days to a few weeks, many of these symptoms subside and since insulin and blood sugars stay super stable, and fats are satiating, energy, hunger and cravings can be positives of this diet.

In the long term, there are some considerations that question the safety of the diet. Given the restrictive nature of the diet including limited grains, fruits and some veggies, possible nutrient deficiencies exist including fibre, calcium, vitamin D, and B vitamins. There are also some potential concerns with kidneys and gut micro biome. In practice, many report challenges with social outings, forcing the question of its long term sustainability and risks of disordered relationships with food.

Does it lead to fat loss?

More than likely. Similar to all carb restricted diets there’s suddenly no more bagels, muffins and bowls of pasta with cream sauce, so go figure. Water loss will be significant via glycogen losses so this also makes up at least 5 pounds. Fat will come off too because hunger is controlled and in the absence of carbs, the body feasts on other stores including fat. Due to the insulin and blood sugar stability there can be great response to this if there’s underlying metabolic disorders.

On the cons side, maintaining and building lean mass is often difficult, if at all possible. This is a major problem for athletes and non athletes as this is what helps us keep our resting metabolism high. Loss of lean mass and difficulty with muscle gains is probably the biggest downfall of this diet. As a result, nutrient timing around exercise and getting in sufficient protein is necessary. Remember though that too much protein and you will be out of ketosis, so this presents a challenge for some.

Keto and Performance goals: A summary of the evidence

For strength or high intensity training, Keto is not recommended and has shown to impede performance in these types of sports. Building lean muscle mass on Keto is quite difficult given the low carb and moderate protein availability which is necessary for recovery and the anabolic response. For these reasons, it is a questionable choice for power athletes including weightlifters, field sports, sprinters, rowers and possibly ineffective for even the recreational athlete seeking sustained fat loss and lean gains.

Fat is also undoubtedly NOT the most efficient fuel source when performing anaerobic exercise. Meaning, that physiologically high intensity activities will not fare well under these conditions and well-timed carbs are the preferable choice. This is a fact.

For endurance athletes using this diet there are 3 main proven training benefits.

1.Your body does adapt to using triglycerides better after a period of 5 days to a few weeks

  1. Further improvements to be had after being very low carb or in ketosis after longer periods of time (weeks to months).
  2. Less fuel required during long races when glycogen stores are low resulting from adaptation to improved fat utilization.

Despite this, the literature does not currently show proven benefits to performance or energy economy. In fact, most recent evidence still shows that higher carb diets win out when it comes to optimal performance in endurance sport, especially as intensity increases. This is an important consideration for elite athletes who can train at higher intensities even at the latter leg of a marathon.  How low can you go without sacrificing performance? This may be highly individual, and sport and goal specific.

Given this mixed information, individualization, periodization and strategic application of high fat low carb diets or Keto is recommended when it comes to endurance training and nutrition intervention. For a customized periodization plan it is important to start implementing this early in your training season so you have lots of time to test the theory and find a program that works for you. Working with your fitness coach and a registered dietitian who specializes in sport nutrition may also be key, to ensure you are meeting your nutrient needs and performing at your best.