Some say that you need fast-digesting carbs after a workout to replenish glycogen, spike insulin and gain muscle.
But, you may also come across claims that taking in carbohydrate after exercise will stop you burning fat.
If I wanted to make a case for the importance of taking in carbs after a workout, it would go something like this:
After a tough workout, your body is depleted of glycogen – the name given to carbohydrate stored in your body – which needs to be replaced as soon as possible. Failure to do so is cheating your muscles and putting the brakes on recovery.
Stored glycogen in muscle cells will also pull water into those cells. This increases cell volume, triggering changes in the muscle that will ultimately lead to faster growth.
The best way to do this is with a rapidly digested carbohydrate with a high glycemic index. Dextrose, maltodextrin, waxy maize starch or Vitargo will all do the job.
The carbs also jack up your insulin levels, which helps to shuttle nutrients into muscle cells, as well as blocking the post-exercise rise in cortisol levels, which would normally have a catabolic effect on your muscles.
In short, to truly maximize recovery and muscle growth, carbs after a workout are essential.
Insulin will be spiked, cortisol will be shut down, and glycogen will be restored as the post-workout gods deliver you directly to recovery heaven.
Or will they?
Actually, they won’t.
It’s true that muscle glycogen is synthesized more rapidly if you take in some carbs immediately after a workout rather than several hours later.
In fact, delaying the consumption of post-workout carbs for just two hours has been shown to slow the rate of muscle glycogen resynthesis by as much as 50% .
But as long as you’re getting enough carbohydrate in your diet, glycogen levels will return to normal after a day or two, regardless of when that carbohydrate is consumed [1, 2] .
Put differently, the speed of post-exercise glycogen synthesis is not important as long as the total carbohydrate need for the day is met.
Unless you’re doing multiple daily workouts, a decent muscle-building diet will provide enough carbohydrate to restore glycogen regardless of whether or not it’s taken immediately after training.
Think of it like putting fuel in your car.
Unless you were taking part in a race, the rate at which the pump dispenses the fuel into your car is of very little practical significance.
What’s most important is the amount of fuel that gets into the tank, rather than the speed at which it gets in there.
It’s a different story if you’re involved in a sport or activity where the length of time between exercise is relatively short.
The training practices of some athletes, for example, will often demand multiple bouts of exercise targeting the same muscle groups on the same day.
In this case, speeding up the rate at which glycogen is replenished takes on a much greater importance . You want those muscles ready for action again as soon as possible.
In other words, the speed of glycogen restoration is important for some people in certain circumstances.
But for most of us, it isn’t.
The idea that you need carbs after a workout to “spike” insulin levels and gain muscle is also a myth.
That’s because protein by itself will raise insulin levels. Whey protein, for example, has a much bigger impact on insulin levels than even pure glucose .
But this has little to do with changes in blood sugar levels. Rather, the amino acids in whey trigger insulin secretion directly in pancreatic beta cells. The branched-chain amino acids, leucine in particular, appear to be the most potent insulin secretagogues.
Whey also stimulates the release of a couple of gastrointestinal hormones known as GIP and GLP-1, both of which have the effect of raising insulin levels .
In one study, taking 50 grams of carbohydrate with 25 grams of whey protein after exercise failed to stimulate muscle protein synthesis or inhibit protein breakdown to a greater extent than 25 grams of protein alone .
The rise in insulin from protein alone is enough to inhibit the increased rate of muscle protein breakdown that normally happens after training with weights .
In other words, if you’re taking in a reasonable amount of protein after training, the addition of carbohydrate isn’t going to help you gain muscle any faster.
Dig through the research, and you’ll find very little evidence to show that the addition of post-workout carbs to a protein shake has any additional muscle-building benefits compared to the protein shake alone [4, 14].
What about fat loss?
You may have heard that taking on board fast-acting carbs after a workout will sabotage your attempts to get lean.
The research on the subject is a bit of a mixed bag. Some studies show that taking in carbs after a workout puts the brakes on fat burning, while others show that it has no effect.
One trial, which looked at fat metabolism for three hours after a post-workout meal or plain water, shows little difference in the number of fat calories burned .
A study published in the British Journal of Nutrition shows that fat oxidation remains high even when a large bowl of pasta is eaten after exercise .
On the flip side, Colorado State University researchers found a marked drop in fat oxidation when a carbohydrate-rich mixed meal was consumed immediately after exercise .
A Canadian team also found that replacing the calories burned during exercise with a post-exercise milk shake limits the normal rise in fat metabolism that occurs after a workout .
However, all four of these studies have limited practical application, and here’s why.
If you really wanted to establish the effect of carbs after a workout on fat loss, you’d need to look at changes in body composition over a period of 2-3 months. Measuring fat metabolism during a narrow window of time immediately after exercise gives you a very limited picture about what’s going on.
To lose fat, all you need is an energy deficit. As long as a post-workout meal/shake doesn’t reduce or eliminate that deficit, it’s not going to slow your rate of fat loss.
In summary, there’s nothing wrong with taking in carbs after a workout.
It’s not going to stop you losing fat.
But nor will it make a great deal of difference to the speed at which you gain muscle, and is not as vital as was once believed.
SEE ALSO: THE FLAT BELLY CHEAT SHEET
If you want less flab and more muscle when you look down at your abs (or where they should be), check out The Flat Belly Cheat Sheet.
It's a “cut the waffle and just tell me what to do” PDF that tells you exactly how to get rid of belly fat. To get a copy of the cheat sheet sent to you, please click or tap here to enter your email address.
ABOUT THE AUTHORChristian Finn is the nation’s leading authority on science-based, joint-friendly ways to build muscle. A former "trainer to the trainers," he holds a masters degree in exercise science, and has been featured in or contributed to major media on two continents, including the BBC and Sunday Times in the U.K. and Men’s Health and Men’s Fitness in the U.S.
1. Parkin JA, Carey MF, Martin IK, Stojanovska L, Febbraio MA. (1997). Muscle glycogen storage following prolonged exercise: effect of timing of ingestion of high glycemic index food. Medicine and Science in Sports and Exercise, 29, 220–224
2. Wojcik, J.R., Walber-Rankin, J., Smith, L.L., & Gwazdauskas, F.C. (2001). Comparison of carbohydrate and milk-based beverages on muscle damage and glycogen following exercise. International Journal of Sports Nutrition and Exercise Metabolism, 11, 406-419
3. Staples AW, Burd NA, West DW, Currie KD, Atherton PJ, Moore DR, Rennie MJ, Macdonald MJ, Baker SK, Phillips SM. (2011). Carbohydrate does not augment exercise-induced protein accretion versus protein alone. Medicine and Science in Sports and Exercise, 43, 1154-1161
4. Figueiredo VC, Cameron-Smith D. (2013). Is carbohydrate needed to further stimulate muscle protein synthesis/hypertrophy following resistance exercise? Journal of the International Society of Sports Nutrition, 10, 42
5. Aragon AA, Schoenfeld BJ. (2013). Nutrient timing revisited: is there a post-exercise anabolic window? Journal of the International Society of Sports Nutrition, 10, 5
6. Jentjens R, Jeukendrup A. (2003). Determinants of post-exercise glycogen synthesis during short-term recovery. Sports Medicine, 33, 117-144
7. Bosher, K.J., Potteiger, J.A., Gennings, C., Luebbers, P.E., Shannon, K.A., & Shannon, R.M. (2004). Effects of different macronutrient consumption following a resistance-training session on fat and carbohydrate metabolism. Journal of Strength and Conditioning Research, 18, 212-219
8. Folch, N., Peronnet, F., Massicotte, D., Duclos, M., Lavoie, C., & Hillaire-Marcel, C. (2001). Metabolic response to small and large 13C-labelled pasta meals following rest or exercise in man. British Journal of Nutrition, 85, 671-680
9. Long W 3rd, Wells K, Englert V, Schmidt S, Hickey MS, Melby CL. (2008). Does prior acute exercise affect postexercise substrate oxidation in response to a high carbohydrate meal? Nutrition and Metabolism, 5, 2
10. Dionne, I., Van Vugt, S., & Tremblay, A. (1999). Postexercise macronutrient oxidation: a factor dependent on postexercise macronutrient intake. American Journal of Clinical Nutrition, 69, 927-930
11. Nilsson M, Holst JJ, Björck IM. (2007). Metabolic effects of amino acid mixtures and whey protein in healthy subjects: studies using glucose-equivalent drinks. American Journal of Clinical Nutrition, 85, 996-1004
12. Borsheim, E., Cree, M.G., Tipton, K.D., Elliott, T.A., Aarsland, A., & Wolfe, R.R. (2004). Effect of carbohydrate intake on net muscle protein synthesis during recovery from resistance exercise. Journal of Applied Physiology, 96, 674-678
13. Salehi A, Gunnerud U, Muhammed SJ, Ostman E, Holst JJ, Björck I, Rorsman P. (2012). The insulinogenic effect of whey protein is partially mediated by a direct effect of amino acids and GIP on β-cells. Nutrition & Metabolism, 9, 48
14. Hulmi JJ, Laakso M, Mero AA, Häkkinen K, Ahtiainen JP, Peltonen H. (2015). The effects of whey protein with or without carbohydrates on resistance training adaptations. Journal of the International Society of Sports Nutrition, 12, 48