Bringing context into nutrient timing

Nutrient timing is a broad concept and, like everything else, depends on context. It gained popularity in 2004 with the publication of a book entitled Nutrient Timing: The Future of Sports Nutrition (Drs Ivy and Portman). But as we delve deeper into the research, we realise that nutrient timing is not so clear-cut.

Post-exercise
Nutrient timing is probably best known for its ‘anabolic window’ or ‘window of opportunity’. This theorises that the body is most responsive to carbohydrates and protein immediately after exercise until 60 minutes post-exercise – carbohydrates for quick glycogen restoration and protein to stimulate muscle protein synthesis for repair.

In theory, that makes sense. But this is where context comes into play:

Research has shown that glycogen restoration is faster when carbohydrate is available immediately after exercise and this effect lasts about 30 to 60 minutes, mainly because of greater insulin sensitivity and the upregulation of GLUT4 receptors (1). Yet, restoring glycogen as quickly as possible is only really important if athletes are training more than once a day (less than four hours recovery time), or competing in several events a day or over a short period. If there is no pressure for the athlete to perform on the same day, ingesting carbohydrates immediately after their training session is less important because there is enough time to restore glycogen during the day with each meal.

However, if an athlete is looking to upregulate fat oxidation, glycogen availability should be reduced, and they can do this in several ways, including not consuming carbohydrates in the recovery period or limiting carbohydrate intake between sessions, so that the first training session lowers muscle glycogen levels for the second training session.

As for protein, we know that athletes need it to stimulate muscle protein synthesis for muscle repair or growth. But research shows that grabbing a protein shake right after a training session is not as important as it seems.

A well-known meta-analysis concluded that what really matters is an athlete’s total daily protein intake (2). A more recent study supports this finding and also highlights that a well-distributed protein intake throughout the day is key (every three to four hours) (3). Per meal recommendations are 20-40g of good-quality protein, with whole-food protein sources potentially containing micronutrients that can continue to enhance the muscle protein synthesis response.

That said, like carbohydrates, if the athlete is training or competing several times a day or within a short period, making sure they ingest protein immediately post-exercise may be more important in terms of total energy intake, plus there is no harm in taking advantage of the ‘anabolic window’.

Pre-exercise
Another important aspect of nutrient timing is what the athlete consumes before a training session or competition. Again, lots of variables come into play here.

In most contexts, athletes should consume a high-carbohydrate meal two to three hours before their training session or competition to support optimal performance. If the athlete only has an hour before their training session or competition, they should prioritise easily digestible foods in the form of a snack low in fibre, which consists mainly of carbohydrates and protein. But again, if the goal is to optimise fat oxidation, having a low-carb meal or training fasted is key.

Hydration is also an important consideration. Athletes should aim to be in an euhydrated state before their training session or competition because optimal hydration maximises blood volume and supports cardiovascular function. Monitoring an athletes’ urine, to ensure that it is pale yellow in colour, is an easy and practical to safeguard they are euhydrated.

On the other hand, training tactically and carefully in a dehydrated state is quite a popular practice nowadays, especially for long-distance runners in the heat, despite limited evidence (4). It is thought to be an effective way to train the body how to tolerate the effects of dehydration by stressing it to stimulate blood volume expansion and benefit from a psychological perspective, improving tolerance to exercise.

Ergogenic aids
Another aspect to consider within pre-event nutrient timing are ergogenic aids such as caffeine, creatine and beta-alanine.

Let’s take caffeine as an example: it is known to enhance performance in endurance-, strength- and power-based sports, and helps to improve focus and reduce tiredness. It is mostly effective when consumed within the hour before a training session or competition (3 to 6mg/kg body weight), and tends to peak 90 minutes post-ingestion (5).

But more recent research highlights how much the success of caffeine depends on the genetics of the individual. Athletes who are not genetically suited to processing caffeine (‘slow metabolisers’) should minimise/avoid caffeine or pick decaffeinated drinks instead. Research shows that athletes in this group can hinder their performance if they ingest too much caffeine before a race (6).

As you can see, nutrient timing is a sophisticated concept that must be brought into context. There are certain situations in which this concept can be valuable for an athlete, but there also many times when it is unnecessary, causing athletes to obsess about getting their timing right, while overlooking the basics, such as daily energy intake and food quality. Then again, nutrient timing is not harmful and might be a strategic way to ensure that an athlete is meeting their daily energy requirements.

References:

  1. Jentjens R & Jeukendrup A (2003). Determinants of post-exercise glycogen synthesis during short-term recovery. Sports Med. 33(2):117-144.
  2. Schoenfeld BJ, Aragon AA & Krieger JW (2013). The effect of protein timing on muscle strength and hypertrophy: a meta-analysis. J Int Soc Sports Nutr. 10(1):53.
  3. Trommelen J, Betz MW & van Loon LJC (2019). The Muscle Protein Synthetic Response to Meal Ingestion Following Resistance-Type Exercise. Sports Med. 49(2):185-197.
  4. Akerman AP et al (2016). Heat stress and dehydration in adapting for performance: Good, bad, both, or neither? Temperature (Austin). 3(3):412-436.
  5. Goldstein ER et al (2010). International society of sports nutrition position stand: caffeine and performance. J Int Soc Sports Nutr. 7(1).
  6. Guest N et al (2018). Caffeine, CYP1A2 Genotype, and Endurance Performance in Athletes. Med Sci Sports Exerc. 50(8):1570-1578.