Metabolic Efficiency refers to the measure of how well the Body utilises fat as an energy source. The human body is able to store around 1,200-2,000 calories in the form of carbohydrates (glycogen) split between the liver, muscles, and blood. These stores would allow us to exercise at a low to moderate intensity for around 2 or 3 hours.

However, there is another source of energy that the human body can store that could provide up to a staggering 80,000 calories: fat. What would happen if we were able to teach our body to use fat stores for energy instead of depleting our carbohydrate resources? 

The benefits of Metabolic Efficiency Training

Metabolic Efficiency Training was a concept developed by Bob Seebohar in 2003 and refers to teaching our body to use fat as a primary energy source. This has a number of positive implications:

• If the body is able to use fat to produce energy, racing athletes can become less dependent on carbohydrates.
• Less carbs means a lower probability of GI distress (stomach cramps being a common issue among endurance athletes).
• More fat burnt means less body fat and a leaner frame, a positive impact on performance for endurance athletes.

It's key to understand when the body uses fats or carbohydrates as its primary energy source. Typically, short-duration exercises will use carbohydrates, while longer endurance exercise will cause the body to start burning fat. This happens during aerobic training when the intensity is close to the aerobic threshold or lactate threshold.

In order to be 100% accurate, Bob Seebohar described a lab test known as “crossover point”.  This is the exact point during an aerobic session when the body stops using fat as an energy source and moves to burning carbs as its energy source.

How to achieve Metabolic Efficiency

As not everyone has access to a lab where this test can be performed, there is a way to teach the body to be more efficient. There are a few rules that everyone can follow. This is best performed at the beginning of the training season, when the athlete is building an aerobic base.

• Avoid high-calorie carbs such as pasta, rice or white bread. During this period, all carbs should come from vegetables and fruit. Also during this phase, more good fats (omega 3 or 6) and proteins should be consumed.
• Avoid sport supplements such as gels or bars which are high in carbs.
• Practise training in a fasted state, building up the duration of the training sessions slowly until you're able to complete up to 3 hours on only water. These session must be endurance-based and performed at a low intensity.
• After training, avoid recovery drinks and high glycemic index carbs. If the training session was easy, theoretically the body used fat as its primary fuel source and so carbohydrates won't need to be replenished. 

By following the aforementioned rules, the body will become more efficient and better at using fats as an energy source.

Which foods to eat when training for Metabolic Efficiency:

• Protein: poultry, tuna, salmon, mackerel, eggs whites, whey protein or plant protein.
• Low glycemic carbs: spinach, tomatoes, kale, lettuce, cauliflower, carrot, beans, sprouts.
• High glycemic carbs: oats, quinoa, potatoes, whole wheat bread, rice, pasta.
• Fats: avocado, coconut oil, olive oil, egg yolk, nuts, peanut butter, almond butter.

About the author: Cesar Martinez is an Ironman athlete.