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Weight management: is protein better than nothing?
SPB looks at new research on pre-exercise protein intake and explains how it could be a valuable tool for weight management
There’s no arguing with the science of exercise physiology and sports nutrition; if maximising your performance on the day, or later that week is your goal, you need to ensure you’re getting adequate carbohydrate before, during and after exercise. However, over recent years a number of researchers have begun to speculate that always training with ample carbohydrate available to the working muscles might not be the best way to produce fitness gains in the longer term – ie over weeks and months. This thinking helps explain the rise in popularity of the ‘train low, race high’ theory, which is practiced by many athletes today.
Thrifty genes
Basically the train low, race high’ theory says that because humans evolved as hunter-gatherers in an environment where carbohydrate was not freely available, our ancestors made use of so-called ‘thrifty’ genes in the muscles. By improving fat metabolism and prolonging endurance, these thrifty genes would have enabled our forebears to hunt, run and survive without muscles crammed full of carbohydrate (glycogen).
Compared to our ancient forebears, 21st century humans have it easy. With modern agricultural practices and no need to hunt and forage for food, most of us have free access to food, 24/7. Now compare our feeding habits to our hunter-gatherer ancestors. Although they managed to sustain themselves, they would have periodically faced periods of famine when food was in scarce supply. Even during periods of relative abundance, there would have been short periods of time – perhaps just a day or two - with no access to food. Today we call this fasting – back then it was just the reality of life!
What’s fascinating is that there’s convincing evidence that our genetic makeup has remained essentially unchanged over the past 10,000 years, which almost certainly has profound implications for today’s athletes. In recent years, a number of these thrifty exercise genes involved in the adaptation to exercise and training have been identified, and some of them are affected by the biochemical environment in the muscle – for example, how much muscle glycogen is present or circulating glucose levels when exercise is performed(1-3).
Weight management and training low
Many scientists are now convinced that (thanks to our thrifty genes), lower levels of muscle glycogen during training might stimulate certain metabolic pathways in the body, resulting in enhanced fat burning and better muscular adaptation to training(4). The evidence is actually very persuasive; numerous human and animal studies have shown that curtailing carbohydrate intake before and during exercise enhances the rate of fat oxidation and the proportion of energy that is derived from fat, thus sparing muscle glycogen reserves and helping to reduce body fat(5-10).
Low-carbohydrate training options
If low-carbohydrate training delivers fat-loss benefits and ‘teaches’ muscles to conserve glycogen, why don’t endurance athletes use this approach all the time? There are two main reasons: firstly, studies show that training in a low-carbohydrate state does not enhance performance in a racing environment. In a landmark study on this topic, a Professor Louise Burke who is a world authority in this area of research concluded that: “Despite increasing fat oxidation and adaptive responses, and reducing the reliance on carbohydrate utilisation during exercise, there is no clear evidence that these (low-carbohydrate) strategies enhance exercise performance”(11). Also, performing high-quality, intense training – the sort that’s proven to significantly enhance aerobic performance – is hard in a glycogen-depleted state!
A second reason is that even allowing for the fat-oxidation/fat loss benefits that low-carbohydrate training brings, there are a number of potential drawbacks. These include:
· Increased secretion of stress hormones leading to lowered post-exercise immunity and increased risk of upper respiratory tract infections;
· Reduced length of training sessions due to fatigue induced by low glycogen (this could be important in preparation for a long-distance event);
· Increased risk of burnout and overtraining;
· Reduced hydration in hot-weather training (some carbohydrate in a drink can help transport fluid from the gut into the body);
· Increased muscle tissue damage and breakdown, leading to potential losses in muscle mass;
· Possible strength losses in sports where simultaneous strength and endurance training is required.
Minimizing low-carbohydrate drawbacks
Is it possible to incorporate some of the potential gains of low-carbohydrate training (ie increased fat burning), while at the same time ensuring that muscles maintain their carbohydrate burning efficiency and are able to perform intense training sessions – a sort of halfway house? This has been the goal of some researchers, who have been studying alternative approaches to train low – approaches that can help stimulate the thrifty genes and maximise training adaptation, but with fewer drawbacks. Some of these different approaches are outlined in figure 1. Essentially, all these alternative approaches involve strategies where training takes place when muscles are at least partially depleted in glycogen (to activate thrifty genes).
Figure 1: Alternative approaches to chronic low-carbohydrate training
While they vary quite a bit in detail, what they all aim to do is to help athletes to engage in low-carbohydrate training in a relatively convenient and easy manner. For example, training before breakfast in a fasted state (ie no food since early evening before) is something that most athletes can manage without too much inconvenience and hardship. Just get up, have a cup of tea or coffee, do your training then have breakfast when you finish your workout! Unsurprisingly, exercising in an overnight fasted state (ie before breakfast) is a very popular strategy used by endurance athletes, with one study finding that around 63% of athletes incorporate this in their training program occasionally or regularly(12).
Those who struggle
Despite the potential advantages of low-carbohydrate training in terms of weight management, there are many athletes who struggle to engage in this type of training. Typically, these athletes report that subjectively that they feel too hungry or just end up feeling terrible during workouts on a completely empty stomach. Another reason cited by athletes is that training with low carbohydrate availability is known to increase skeletal muscle protein oxidation due to a greater contribution of protein catabolism to energy production(13,14).
In plain English, when carbohydrate is in short supply, the body is able to supplement some of its energy needs by burning protein – protein that comes from the breakdown of muscle tissue. Of course, during exercise – especially intense or prolonged exercise – some muscle tissue damage and breakdown always occurs. However, if this process is exacerbated by regular low-carbohydrate training, the net result over time is likely to be muscle tissue loss, leading to more injury-prone and less powerful muscles – exactly what athletes do NOT need!
A protein solution?
A possible solution to overcome these challenges is the ingestion provision of dietary protein before exercise. Protein is regarded as a nutrient that raises insulin levels, which in theory would reduce fat burning during exercise. However, fairly recent studies on fat oxidation during exercise where protein was consumed beforehand have found that fat burning was not affected compared to fasted exercise(15-18). This raises an interesting question: can consuming protein before exercise still help athletes to burn fat while making that exercise more pleasant subjectively (eg by preventing feelings of hunger) and helping to minimize muscle tissue loss during exercise?
New research
To answer this study, new research by British scientists just published in the Journal of the International Society of Sports Nutrition has compared the effect of consuming different amounts of pre-exercise protein on subsequent fat oxidation during that exercise(19). In a randomized, double-blinded trial, 15 healthy active males and females engaged in regular endurance training completed 1 hour of steady-state cycling on a stationary bike at 60% of their peak power output (moderately hard to hard) on three separate occasions at least 72 hours apart. Each trial was identical except for what the cyclists consumed 30 minutes before each trial:
· 500mls of a strawberry flavored whey protein hydrosylate drink containing 40 grams of protein.
· 500mls of a strawberry flavored whey protein hydrosylate drink containing 20 grams of protein.
· 500mls of a strawberry flavored whey protein hydrosylate drink containing zero grams of protein (the control condition).
The different drinks were disguised to all taste exactly the same and neither the participants nor the researchers knew which drink was being consumed in any trial (ie double blind trial). Because each participant performed a trial in which they consumed the zero-protein drink, they acted as their own controls. During the trials, the cyclists’ heart rates and perceived exertion levels were recorded. In addition, gas analysis was carried out to record the relative amount of fat oxidation during each trial. Before and after each trial, blood samples were also taken to measure the amounts of fatty acids and glucose circulating in the blood (higher fatty acid levels suggest more fat oxidation while higher glucose suggests less). An outline of the protocol is shown in figure 2.
Figure 2: Outline of study design
What they found
The key finding was that although ingesting 20g and 40g of protein before exercise slightly raised insulin levels in the cyclists compared to 0g (ie exercising in the fasted state) and slightly reduced the amount of fatty acids circulating in the blood, this did not affect fat burning rates whatsoever. In short, the cyclists burned just as many fat calories during exercise when they consumed 20g or 40g of protein beforehand as they did without consuming anything. As the one hour trial progressed, fat burning rates gradually increased. But this trend was identical regardless of whether protein was ingested or how much was ingested. See here for a full table of results.
Implications for athletes
Although there’s no substitute for ample carbohydrate feeding before and during an important competitive event, exercising in a low-carbohydrate state does offer a distinct advantage for athletes trying to shed excess lbs, or maintain an optimum racing weight. While many athletes find small doses of targeted low-carbohydrate training quite manageable, a sizeable proportion may struggle to train after several hours or even longer without food. If that describes you, this research on protein intake makes for encouraging reading because consuming pre-exercise protein does not seem to blunt fat burning at all.
In fact, pre-exercise protein ingestion may be even better than training in a fasted state because the availability of protein (amino acids) during exercise may help accelerate the repair and growth of muscle tissue and prevent the loss of muscle mass in the longer term. While the subsequent muscle protein synthesis rates weren’t measured in this study (a shame as it would have been informative), previous research on this subject does indeed show that ingesting protein either before or during exercise helps accelerate muscle repair and growth following exercise – a good thing for any athlete who wants to stay strong!
If you want to try this strategy, how much protein should you ingest and when? That probably depends on your gastric tolerance and your length of workout. Those with more sensitive tummies are probably better off sticking to a 20-gram protein dose taken 30 minutes before training. If your tummy is more robust and you are aiming for a workout longer than one hour, this amount could be increased up to 40 grams. Using the whey hydrosylate protein, there were no reports of gastric distress, even when ingesting the 40-gram dose. Be aware however than other, slower-digesting proteins such as casein, pea and soy may pose more a digestive burden, so they may need to be taken earlier before training and in smaller doses!
References
1. J Physiol 538: 911–917, 2002
2. FASEB J 15: 2748–2750, 2001
3. J Physiol 541: 261–271, 2002
4. J Physiol 541, 273-281, 2002
5. J Appl Physiol 98: 93–99, 2005
6. J Physiol 546: 851–858, 2003
7. Cell 134, 405-415, 2008
8. Horm Metab Res. Jan;40(1):24-8, 2008
9. J Appl Physiol. Nov;105(5):1462-70, 2008
10. J Appl Physiol. May;106(5):1513-21, 20094-9
11. Scand J Med Sci Sports. Oct;20 Suppl 2:48-58, 2010
12. Int J Sport Nutr Exerc Metab. 2020 Sep 1;30(5):345–356
13. J Appl Physiol ( 1985). 2010 Aug;109(2):431–43
14. J Appl Physiol Respir Environ Exerc Physiol. 1980 Apr;48(4):624–629
15. Amino Acids. 2015 Feb;47(2):407–416
16. Nutrients. 2021 Apr 14; 13(4):1291
17. J Int Soc Sports Nutr. 2018 Nov 29;15(1):56
18. Eur J Appl Physiol. 2013 Jun;113(6):1457–1468
19. J Int Soc Sports Nutr. 2023 Dec;20(1):2275006. doi: 10.1080/15502783.2023.2275006
20. J Int Soc Sports Nutr. 2022 Oct 12;19(1):623-637 Sports Med. 2022 Nov;52(11):2713-2732
Andrew Hamilton
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