High Fat Diet: Pros and Cons

HFLC (high fat, low carb) and ketogenic diets have gained a cult following over recent years. Not all that long ago, low fat products (for example, yogurts and cheeses) were the trend, due to the links between fat and cardiovascular disease. Even now, the Eatwell Plate shown in schools promotes a diet of mainly grains, potatoes, fruits and vegetables, with minimal fat.

The complete 180 in mindset around fat is shocking, and more and more research is emerging on the subject. Let’s discuss the pros and cons of a low carb lifestyle.


Why we should all be eating enough fat

  • Source of fat soluble vitamins A, D, E and K
  • Source of essential fatty acids
  • Insulation
  • Brain function
  • Among other reasons!


Burning and storing fat

As the largest of the 3 macronutrients (hence fat being more calorie dense than carbohydrates and protein) the average person’s body will avoid using it for energy. The process of breaking down fats is known as lipolysis.

As a rule of thumb, your body will first oxidise any alcohol in the system, then protein, CHO and finally fat. Fat that is not used will be stored as adipose tissue.



Keto for athletes

While there are some great testimonials for the keto diet from fairly sedentary individuals who report increased satiety and reduced cravings, athletes with performance goals over physique ones may not reap as many benefits.

Two studies on athletes following a ketogenic diet concluded that the athletes experienced a lag in performance across the first week or two of carbohydrate restriction, after  which  both  peak  aerobic power and sub-maximal (60–70% of VO2max) endurance performance were restored (Phinney, 2004). Note, restored, not improved, suggesting that there is no reason to implement it. The initial adaption period is commonly reported in those converting to the diet.

This links into another issue with the ketogenic diet- you are only in ‘ketosis’ if you keep up the extremely low carbohydrate intake indefinitely. Cheat meals of pizza and cookies on a weekend invalidate what you are trying to achieve from the diet.

Ketosis is a metabolic state in which some of the body's energy supply comes from ketone bodies in the blood, in contrast to a state of glycolysis in which blood glucose provides energy. Ketosis is a result of metabolizing fat to provide energy.

Another 2012 study on elite gymnasts by Paoli et al* found that No significant differences were detected between keto and the Western diet in all strength tests. However, a significant amount of body fat and weight were lost, with no significant change in muscle mass.

Exercise stimulates the breakdown of fat which helps mobilise it for energy towards performance. Intramuscular fat is easier to use as fuel for exercise than adipose tissue, but adipose tissue will be used first, and most of the population have excess of this. For this reason, there is some argument that high fat can be a good option for lean, elite athletes such as long distance runners. Care should still be taken as fat close to training can cause GI distress (diarrhoea, bloating, sluggishness).



There may be links between fat/weight loss and keto, although muscle mass and performance are unlikely to improve. Ultimately, if you are able to stick to such a strict diet and enjoy it long term, it may be worth doing. If you are more likely to adhere to a calorie controlled diet which prioritises carbs for fuel, calorie intake is the determining factor of weight loss/gain, not macronutrient split.


* Paoli, A., Grimaldi, K., D’Agostino, D., Cenci, L., Moro, T., Bianco, A., & Palma, A. (2012). Ketogenic diet does not affect strength performance in elite artistic gymnasts. Journal Of The International Society Of Sports Nutrition, 9(1), 34. http://dx.doi.org/10.1186/1550-2783-9-34

About the Author

Savannah Westerby, BSc Sport and Exercise Nutrition. IG:@savannahwesterby
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