What is a low carb high fat diet?

19 August, 2017

WHAT IS A Low Carb High Fat DIET?

Low carbohydrate, high fat diets (LCHF) such as The Banting, Atkin’s, Paleo, Dukkan, and others, have become popular in the community promising weight loss and health benefits. Typically these diets are composed of meats, fish, dairy, eggs, vegetables, some fruits, and nuts while starches such as cereals and grains, as well as sugars are avoided. A LCHF diet is composed of approximately. 20% or less energy from carbohydrates, significantly lower than current recommendations and 60% of energy consumed as fat, far higher than the recommended amounts.


  • Breakfast – 2 eggs, with bacon and tomato
  • Lunch – large salad with some chicken or fish with cottage cheese
  • Dinner – Stir fry vegetables and meat with a cauliflower rice
  • Snacks – Greek yoghurt, fruit, nuts


The theory of the LCHF diet is that it can tap into the abundant energy source of body fat and conserve carbohydrate, therefore offering an unlimited energy supply for exercise as well weight and health advantages.

While debate continues regarding the general community health benefits of these types of diets, some elite sports people are consuming a LCHF diet due the popularization by athlete anecdotes of improved performance via adapting to ketosis, a process by where the body breaks down fats into ketones to be an additional source of energy to the brain and muscle.

The human body has two main energy reserves to draw on. The relatively unlimited supply of energy from fat found in within the muscle, blood fats and body fat stores and the limited muscle and liver glycogen stores from carbohydrate.

Even a lean athlete has as much as 5kg of body fat stored for energy whereas the glycogen stores are limited to about a tenth of that therefore the idea of being able to use fat as a reliable energy source is very attractive.


The body has to go through an adaptation period from using carbohydrates as a primary energy source to using fat. This is known as fat or ketogenic adaptation which takes approximately 2-3 weeks.

Oxygen must be available to use fat as an energy source (aerobic activity) and fat cannot be utilized for energy without oxygen (anaerobic activity). Fat can be a great fuel for low to moderate endurance type activity such as distance running, distance swimming or swimming training. Endurance training enhances fat oxidation and research has shown a LCHF diet improves this further. The research has also shown the LCHF diet impairs the athlete’s ability to use glycogen which is essential anaerobic activities such as the high intensity break away, sprint or power bout.

Unfortunately to date, the studies looking at performance have been under whelming. Most research has been completed with cyclists, not swimmers and has not convincingly found improvement in performance.

There may be some advantages in a dietary periodization where athletes go through times of LCHF and times of higher carbohydrate eating to optimize muscle use of both fat and carbohydrates as fuels.


Advantages of LCHF eating

  • Possibly better endurance for submaximal training
  • Possibly helpful for longer distance swimming
  • Using LCHF periodically during training may offer benefits to muscle fat oxidation
  • May be helpful for weight
  • Adaptation takes 2-3 weeks and may interfere with training schedule

Disadvantages of LCHF eating

  • Fatigue during adaptation
  • Increased perception of effort with training
  • Possible impaired high intensity competition performance
  • Diet food availability being easily assessable and convenient
  • Current scientific literature does not support benefits


It really depends on the sport, for example an activity like competitive swimming is primarily a power based sport, relying on carbohydrate dependent anaerobic energy in competition, LCHF eating is not recommended as a nutrition strategy for competition.

There may be times in the training schedule where trialing dietary periodisation with LCHF away from competition to see how the athlete responds.

A dietary periodisation protocol would consist of following a LCHF diet for five to six days (the fat adaptation) and then a rest day consuming high carbohydrates.


  • Vary energy intake with training phases and according to the training load
  • Consume adequate carbohydrate to meet training demands.
  • During long training session consume adequate fluid and carbohydrate for hydration and energy.
  • Consume approximately 20-25 grams of protein along with some carbohydrate soon after key training sessions. Examples may include post training snacks:
    • Tub of Greek yoghurt and fruit
    • 600ml skim milk and banana smoothie
    • 600ml skim chocolate milk
    • 100g scrambled tofu on toast
    • Protein shake with fruit
    • 2 eggs on toast
    • 100g fish plus some fruit
  • Possibly consider buffering supplements to reduce acidity from lactic acid build up during anaerobic activity, this may include the use of bicarbonate. Buffers may improve performance and reduce muscle fatigue. Be aware stomach upsets can occurs with higher dose, should be trialed away from competition.
  • Caffeine, if tolerated, may improve performance.
  • Choose a pre-competition meal or snack that you know you will perform comfortably.
  • If multiple heats or events on the one day ensure you have adequate fluids and suitable foods available.



Sports Nutrition – From Lab to Kitchen by Asker Jeukendrup published by Meyer and Meyer Sport

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