With all the debate around the best diets for muscle growth, fat loss and general health, you’ll likely hear a lot about the importance and relevance of nutrient timing.

The principle of nutrient timing is based on the biology and physiology of the human body as the body cycles through phases of tissue building (known as anabolism) and tissue breakdown (known as catabolism) throughout the day.

As such, the theory suggests that you can boost your weight-loss efforts by keeping hormonally-driven fat-loss processes turned on for longer while still supporting muscle repair and recovery by eating the right combination of macronutrients at the right times.

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Three nutrient timing phases

This theory was popularised by respected scientists Dr. John Ivy and Dr. Robert Portman, who authored the book Nutrient Timing: The Future of Sports Nutrition in the early 2000s. This became the reference guide to most sports nutritionists for the past decade.

In the book, Ivy and Portman outline three critical times of the day when nutrient timing is of utmost importance. These phases are the energy, anabolic and growth phases.

The energy phase: Occurs during the workout when energy demands are highest. These demands are met by either ingested nutrients and/or stored nutrients.

The anabolic phase: Occurs immediately after a workout and lasts for up to two hours. This phase is generally termed the “anabolic window” because muscle cells are most receptive to ingested nutrients during this time due to heightened insulin sensitivity and the resultant increase in a cell’s ability to absorb nutrients (through increased membrane permeability).

This is why it is important to get some protein along with some carbohydrates soon after a training session to ensure glycogen and amino acids can get to muscle cells to support growth, repair and recovery.

The growth phase: The 18-20 hours after an exercise session, which includes sleep, when muscle repair and growth occur. The aim during this phase is to prolong and promote additional anabolism through your diet by continuing to get sufficient protein.

However, it is generally advised that you eat more fat and fewer carbs during this period as immediate energy demands are lower.

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The ‘when’ and ‘what’ of nutrient timing

The key to understanding the science of when and what to eat centres around the hormonal changes in the body that happen due to a number of factors.

For instance, glucose tolerance and insulin sensitivity constantly fluctuate during the course of a day due to various factors, including meal timing and meal composition. Exercise also stimulates the release of catabolic and anabolic hormones.

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Carb manipulation

In relation to carbohydrates, the principle of nutrient timing aims to exploit periods of heightened insulin sensitivity – like when you wake up and after exercise – to more efficiently use glucose to fuel tissue repair and replenish depleted energy stores.

Outside of these periods, spiking insulin has the potential to increase fat storage and blunt fat metabolism.

In this context, the nutrient timing approach suggests that you don’t need to eat carbs at every meal. Some would argue that you don’t even have to consume many carbs every day, depending on your activity levels (these people typically follow a carb cycling diet), as long as you consume sufficient carbs on days when your energy or recovery demands are greatest.

Eating most, if not all of your daily carbs after your training sessions (known as carb backloading) can also help to reduce the amount of fat you store, while promoting greater fat loss as your body is more likely to tap into fat reserves during the day for the energy it needs.

Furthermore, some form of carb restriction and/or manipulation will help to restore insulin sensitivity. When this happens, you can reduce your body’s propensity to store excess calories as fat around your midsection after your other meals.

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Protein timing

In terms of protein, it seems that timing is less important than total intake. While we know there are important times to consume protein, either from a supplement or meal, like first thing in the morning and soon after exercise, research suggests that timing may not be as crucial as previously thought.

In a study published in the American Journal of Physiology – Endocrinology and Metabolism, researchers examined whether the amount and timing of protein consumption made a difference in the body’s net protein gains.

Based on the findings, researchers were able to show that the more protein subjects ate, no matter the timing, the better their bodies were at building muscle.

Subjects who consumed double their RDA of protein increased their rate of muscle protein synthesis (the process by which cells use protein to build muscle) and improved their net protein balance (the difference between muscle protein synthesis and protein breakdown).

Further supporting this view, research conducted by the Department of Kinesiology at the McMaster University, has shown that protein synthesis is double 24 hours after heavy resistance training and only then decreases, returning to baseline after 36 hours.

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Should your time your intake?

Based on the available evidence, it seems applying a nutrient timing strategy to your carbohydrate intake may offer certain benefits for fat loss, body conditioning and exercise performance.

But it seems you don’t need to be too concerned about nutrient timing when it comes to your protein intake. The important factors are the total quantity and quality of your intake.