Nutrient timing and the Glycaemic window.
By Theresa Gray
2nd April 2018
Nutrient timing
Have you ever thought or asked;
“Should I eat before a workout or should I fast?”
Or
“What should I be eating before and after a workout?”
Well you are not alone.
These questions are so often asked that there are many research papers surrounding the topics that science calls “Nutrient timing and the Glycaemic window.”
Nutrient timing simply means eating specific macronutrients in specific amounts at specific times. For example, before, during or after exercise.
Glycaemic window of opportunity: simply implies that there is a window of limited time that exists after training to optimise training related muscular adaptions.
But to first begin the topic, I will cover some basic physiology terms for you to get a better understanding of what is happening within the human body.
Digestion: Breaking down large particles of food into smaller particles which primarily begins in the stomach.
Absorption: The process of taking up nutrients into the blood which primarily takes place in the ileum (small intestine).
Gastric emptying: the amount of time it takes carbohydrates, fats and proteins to move from your stomach to the intestines.
Meals that are high in protein and fat stay in the stomach for longer giving the statement, “Protein keeps you feeling full for longer”, meaning. In contrast, carbohydrates move into the intestines much quicker and absorb much faster.
Enzymes: speed up reactions in the body and are essential keys to digestion as well as exercise metabolism.
Glycogen phosphorylase: is the enzyme responsible for regulating and turning stored glucose (glycogen) into an energy form (glucose) when sugar levels are low. In the human body there are multiple forms found primarily in the muscles and liver and some in the brain.
Glycogen synthase: is an enzyme that helps to convert glucose (blood sugar) into glycogen (storage form of glucose).
Nutrient timing and the Glycaemic window.
Being physically active triggers many chemical reactions and activates enzymes like glycogen phosphorylase and glycogen synthase which remain active in the muscles 30 to 60 minutes following your exercise. In addition, food consumed within this window, pre-exercise and post exercise can restore glycogen relatively fast as a result of the heightened enzymes activity.
Old research supported the “Glycaemic window of opportunity” also known as “Post workout anabolic window” and stated after exercise the beneficial time to consume a high protein, carbohydrate snack was just after training (only up to 30 minutes). However, recent longer term studies indicate that the glycaemic window is actually a whole lot wider that they were lead to believe, up to a whole 2 hours after training to receive the full benefits. This means there is much more time for you to consume a wholefood meal rather than throwing back a waxy maize starch and whey hydrolysate shake immediately after training.
Now let’s go back to the original question
Question 1: “Should I eat before a workout or should I fast?”
It all depends on time. What time do you get out of bed? What time of the day do you exercise?
Eating food before exercise is only practical if your food has time to digest and be adsorbed. In other words you need to time your food consumption so that it becomes available fuel for your exercise. In addition, the time required to digest and absorb food also depends on the type and quantity of food consumed. For example, foods high in fat, protein and fibre take longer to digest in the stomach and as a result may trigger stomach discomfort whilst exercising. Additionally, eating a large meal will also take longer to digest and may cause discomfort than say a small snack. So, if you are planning a low intensity workout, such as a bike ride, Tai chi, walking or yoga then eating food before your activity may be better tolerated, in contrast to a high intensity cardio workout, like running. This does not only disagree with a full belly as your stomach contents are being jostled about, but may also lead to further discomfort. Therefore, a standard guide is to have a meal 2.5 to 4 hours before exercise or a light snack 1 to 2 hours before.
So simply put, if you exercise early in the morning like I do, around 8 to 8.30am then it may be best to have your breakfast around 5.30 to 6am. However, if you decide to get out of bed 1/2 hour before you exercise than you may want to skip breakfast and have a very light snack and hydrate on water.
When it comes to nutrition timing listen to your body’s needs.
There is no hard and fast rule that will satisfy everyone.
For example, I need to eat before I exercise to obtain optimal performance, so I don’t feel sluggish and that I can push through to either achieve or push past my exercise goals. In comparison, other people may feel alright to have a light snack to get through their exercise needs.
By paying attention to what works best for you during exercise and how you feel is of great importance. So, if you're a person that needs to eat before a workout but you get out of bed half an hour before exercise, you may need to change your timing and routines to establish your nutrition and exercise combo. Such as, getting up earlier to consume a healthy breakfast or change the plan, sleep in to your normal time and exercise a little later in the day. Thus, by listening to your bodies needs to reach your goal, you may need to work on a plan that works best for you and in your favour.
Need some ideas, try these foods which are sufficient to eat 3-4 hours before exercise:
Toast with jam or honey with a glass of milk
Baked beans on toast
A boiled egg and some toast
Breakfast cereal with milk
Baked potato and cheese with a glass of milk
Plain yoghurt, around 6 to 12 nuts and a piece of fruit
Salad sandwich with meat filling
Pasta or rice dish that is not creamy but sauce based with vegetables.
Or try the following to eat 1 to 2 hours before exercise:
Milk shake or fruit smoothie
Muesli bar
Cereal with milk
Fruit flavoured yoghurt
A piece of fruit.
Question 2:
“What should I eat before or after exercise?”
Pre exercise
Before working out you will want to receive food that sustains energy, boosts performance, hydrates you, preserves muscle mass and helps aid with recovery.
Carbohydrates before exercise provides the energy needed to keep you fuelled at your best and also helps with recovery. In addition, ensuring some carbs are in your system can improve high intensity performance. Moreover, carbohydrates can preserve muscle and liver glycogen and stimulate the release of insulin which therefore prevents protein breakdown from your own muscles.
Re-consider foods that are high in fat and fibre as research suggests that this can lead to increased risk of gastrointestinal discomfort whilst exercising. In contrast, other research suggests consuming fat before exercise does not seem to improve nor impair performance and does not fuel performance. But, fat does slow down digestion which keeps blood sugar and insulin in check in addition to providing some vitamins and minerals. Thus, listen to what your body requires.
So for most activities, carbohydrates and fluid are nutrients most recommended for pre-exercise. However, you may also wish to include some protein (no more than 20 grams) especially if you are training in the morning and your goal is to improve muscle mass and muscle gain.
Pre-exercise for nutrient timing
Eating protein in the few hours before exercise can help maintain or increase muscle size and can reduce markers of muscle damage. In addition, protein can flood your blood stream with amino acids just as your body needs them most. However, when I speak of protein here I am describing protein from a food source such as milk, nuts, eggs or meat not of a high protein shake.
Thus, depending on your individual needs the answer really comes down to just having a normal meal in the couple of hours before exercise. Although, if you don’t have a couple of hours but may still like to eat something, have a smaller meal or snack before your session.
During exercise.
The most important thing to drink whilst exercising is water to keep you hydrated. Apart from long endurance athletes that need to refuel it is not necessary for you to eat during exercise.
Post exercise:
After you have finished your work-out it is imperative that you refuel your body to recover, rehydrate, build muscle and improve your future performance.
Eating protein after exercise stops your muscles in your body breaking down and stimulates regrowth leading to increased or maintained muscle mass. In the past, health experts recommended a fast acting protein like whey or casein hydrolysate products stipulating that the faster you consumed your amino acid fix the better result for your muscles. However, new research suggests that the glycaemic window is actually much wider than originally thought (35 minutes to 2 hours wider) so making a nutritious high protein meal is just as and even more beneficial than a post work out shake. Furthermore, if you consumed protein 2 to 3 hours before your workout, you will already have amino acids ready in available amounts to maximise muscle protein synthesis post workout.
Just remember: High quality protein (meaning all the essential amino acids included) is recommended as long as you eat enough. This means for a man protein consumption consists of 40 to 60 grams and for woman 20 to 30 grams of protein.
Here are a list of protein foods to eat post workout
Eggs
Yoghurt
Cheese
Salmon
Quiche
Nut butters (peanut)
Chicken
Minute steak
Milk
Tuna
Legumes and rice
Carbohydrate consumption is highly recommended after a workout along with your protein as this restores glycogen breakdown. Nonetheless, it is unnecessary to obtain this from refined carbohydrates like from white bread and rice, but rather choose a whole food carbohydrate like some fruit which may be better tolerated, as this restores glycogen and leads to better next day performance.
Although the rate at which you need to replace your glycogen stores really depends on the type of exercise you participate in. For instance, running, swimming and high cardio workouts may need you to consume more carbohydrates than a body builder.
Carbohydrates to be consumed include 0.5 to 0.7 grams per 1.1 to 1.5 kg of body weight. These are the recommended numbers that result in proper carbohydrate stores. For example, 60 kilograms / 1.1kg totals 55 kilograms. 0.6 grams X 55 kilograms totals 33 grams of carbs which equals in food, 2 slices of sourdough rye bread or 1 banana with 125 grams of plain Greek yoghurt.
By choosing the right nutrients to refuel your body will not only maximaise the benefit of your workout but will help in your recovery.
Here is a list of carbohydrate foods to eat post workout:
Flavoured milk
Fruit flavoured yoghurt
Quinoa
Fruit for e.g.: banana and berries.
Rice cakes
Oatmeal
Potatoes/ sweet or white
Pasta
Vegetables and salad
Rice salad.
Example of meals post exercise:
Fruit and yoghurt
Omelette with toast and salad
Tuna and rice crackers
Cereal and milk
Grilled chicken and roasted vegetables
Lastly this infographic explains simply how important nutrient timing and frequency is depending on an individual’s circumstance. Hope it helps answer your burning questions.
https://www.precisionnutrition.com/nutrient-timing
Look out for my recipe A FLUFFY SCRAMBLE EGG WITH LEMON ZEST AND OLIVE OIL SERVED ON A MULTIGRAIN SOURDOUGH
Providing 16 grams protein and 19 grams carbs
References:
Aragon, A. A. & Schoenfield, B. J. (2013) Nutrient timing revisited: Is there a post exercise anabolic window? Journal of the International Society of Sports Nutrition. 10:5
Austin, K. & Seebohar, B. (2011). Performance nutrition. Applying the science of nutrient timing. Human Kinetics Books: Australia & New Zealand.
Australian Sport’s Commission. (2009). Eating before exercise. Retrieved from https://www.ausport.gov.au/ais/sports_nutrition/fact_sheets/eating_before_exercise
Mawer, R. (2017). Does nutrient timing matter? A critical look. Retrieved from https://www.healthline.com/nutrition/does-nutrient-timing-matter
Pierre, B. St. (n.d). Workout nutrition explained. What to eat, before, during and after exercise. Retrieved from https://www.precisionnutrition.com/workout-nutrition-explained
Pierre, B. St. (n.d). Is nutrient timing dead? And does “when” you eat really matter? Retrieved from https://www.precisionnutrition.com/nutrient-timing.
Robinson, J. (2016). What you need to know about nutrient timing. Retrieved from https://www.acefitness.org/education-and-resources/professional/expert-articles/5815/what-you-need-to-know-about-nutrient-timing
Semeco, A. (2016). Post-workout nutrition: What to eat after a workout. Retrieved from https://www.healthline.com/nutrition/eat-after-workout
Wein, D. & Andrews, K. (2011). To eat or not to eat: The truth behind exercising on an empty stomach. National Strength & Conditioning Journal. Volume 10 Issue 5.