The fitness industry is awash with products promising to accelerate weight loss and enhance performance. Among these are post-workout supplements, marketed to increase muscle mass through enhanced muscle repair, recovery, and growth. This article will explore the science behind these supplements, examine their effectiveness, and highlight key considerations for anyone looking to incorporate them into their fitness regimen, using the most recent studies.
Understanding the Basics: Fueling Your Body During Exercise
During physical activity, the body primarily relies on three fuel sources: carbohydrates, fat, and protein. Carbohydrates, stored as glycogen in the liver and muscles, are the most efficient energy source, readily converted into glucose for immediate use by the brain, nervous system, and muscles. The body's glycogen supply typically sustains 90-120 minutes of vigorous activity. Depletion of these stores can lead to fatigue, often described as "hitting a wall." As glycogen diminishes, the body turns to fat for fuel, particularly during low- to moderate-intensity activities. In the late stages of prolonged exercise, when glycogen is scarce, the body may start breaking down muscle protein for glucose production.
Physical activity, especially resistance training, can also induce muscle growth (hypertrophy). Weight lifting causes structural damage to muscle fibers. The body repairs this damage by fusing broken fibers, forming new muscle protein strands, ultimately increasing muscle size.
The Allure of Supplements: Promises and Realities
Workout supplements, including pre- and post-workout formulas, are marketed as crucial for peak performance, fat loss, and muscle growth. The global pre-workout supplement market alone was estimated to reach $13.98 billion in 2020 and is projected to nearly double to $23.77 billion by 2027. However, it's essential to critically evaluate whether these supplements live up to the hype and whether they are necessary or even safe.
Fat burners are dietary supplements that claim to increase your metabolism, reduce fat absorption, or help your body burn more fat for fuel. Manufacturers often promote them as miracle solutions for weight loss. However, according to a 2011 study, fat burners are often ineffective and may even be harmful. There is no miracle pill for weight loss, and even “natural supplements” cannot guarantee fat loss. Everyone’s metabolism is different. The most effective way to lose weight is through regular sleep, decreased stress, regular exercise, and eating a nutrient-rich, healthy diet.
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Post-Workout Supplements: What Are They and What Do They Claim to Do?
Post-workout supplements are designed to aid in muscle repair, recovery, and growth after exercise.
Carbohydrates and Glycogen Replenishment
Replenishing glycogen stores after a workout with sufficient carbohydrate intake is important for muscle recovery, and beginning the next workout with sufficient muscle glycogen stores has been shown to improve exercise performance. However, normal dietary intake is typically sufficient to restore muscle glycogen stores after low-intensity exercises, such as walking, yoga, or tai chi (3-5 g carbohydrate/kg body weight per day), and even for moderate-intensity exercise, such as one hour or more of walking, jogging, swimming, or bicycling at modest effort (5-7 g carbohydrate/kg body weight per day). Post-workout supplementation with carbohydrates and protein within 24-36 hours is only recommended following strenuous physical activity, which includes one hour or more of vigorous exercise such as interval training, running, swimming, bicycling, soccer, or basketball at a moderate to intense effort (where one can only carry on brief conversations or cannot speak); in this case, 6-12 g carbohydrates/kg body weight per day is recommended to be consumed after exercise to fully restore muscle glycogen stores.
Protein: The Building Block of Muscle
Protein is incredibly important for burning fat. Protein can also curb your appetite by increasing the levels of fullness hormones like GLP-1, CCK, and PYY while reducing levels of the hunger hormone ghrelin. A high protein intake can help you burn fat by boosting your metabolism and curbing your appetite. It also helps your body preserve muscle mass. Research has also shown that protein-enriched diets can lead to greater weight loss and improvements in metabolic biomarkers.
Recommended levels of daily protein intake for the general population (0.8 grams of protein for every kilogram of body weight, or about 7 grams of protein every day for every 20 pounds of body weight) are estimated to be sufficient to meet the needs of nearly all healthy adults. Recommendations for protein supplementation during exercise vary based on the type of exercise being conducted: endurance training (e.g., long-distance bicycling) or resistance training (e.g., weight lifting). Very few studies have investigated the effects of prolonged protein supplementation on endurance exercise performance. A review conducted by the International Society of Sports Nutrition found that protein supplementation in the presence of adequate carbohydrate intake does not appear to improve endurance performance, but may reduce markers of muscle damage and feelings of soreness. On the other hand, individuals who engage in high-intensity resistance training may benefit from increased protein consumption to optimize muscle protein synthesis required for muscle recovery and growth, but research is inconclusive, with the majority of studies investigating the effects of protein supplementation on maximal strength enhancement finding no benefit. The extent to which protein supplementation may aid resistance athletes is highly contingent on a variety of factors, including intensity and duration of training, individual age, dietary energy intake, and quality of protein intake. For individuals engaging in strenuous exercise to build and maintain muscle mass, the International Society of Sports Nutrition recommends an overall daily protein intake of 1.4-2.0 g/kg of body weight/day.
Spotlight on Protein Powder
While you can get all the protein you need from protein-rich foods, many people still find it challenging to eat enough protein daily. Protein powder supplements are a convenient way to increase your protein intake. Options include whey, casein, soy, egg, and hemp protein powders. However, it’s important to choose a protein supplement that’s low in sugar and additives, especially if you’re trying to lose weight. Keep in mind that calories are still important. Protein supplements should replace snacks or be part of a meal rather than an extra addition to your diet. This is especially true if you’re trying to lose weight by maintaining a calorie deficit. If you’re finding it difficult to eat enough protein, try taking 1 to 2 scoops (25 to 50 grams) of protein powder per day. The recommended daily intake of protein will vary based on your activity levels, age, sex, weight, height, etc. That said, the Recommended Dietary Allowance (RDA) for protein is 0.8 grams of protein per kilogram of body weight.
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Powdered protein can come from a variety of sources, including eggs, milk (e.g., casein, whey), and plants (e.g., soybeans, peas, hemp). Some protein powders contain protein from multiple sources; for instance, a vegan option might include protein derived from peas, pumpkin seeds, sunflower seeds, and alfalfa. Protein powders are dietary supplements and are not reviewed by the FDA for safety or effectiveness. They can often contain non-protein ingredients, including vitamins and minerals, thickeners, added sugars, non-caloric sweeteners, and artificial flavoring.
Whey Protein
Casein and whey are proteins found in cow’s milk; roughly 80% of milk proteins are casein, while the other ~20% are whey. Both proteins should be avoided by people who have trouble digesting dairy. Casein and whey contain all essential amino acids and are easily absorbed by the body, but their speed of absorption differs. Whey protein is water soluble and rapidly metabolized into amino acids. Studies examining protein supplementation for resistance training suggest that whey’s faster digestion could be beneficial for gains in skeletal muscle mass compared to casein in both young men and in trained bodybuilders. Preserving muscle is priority one, and nothing beats whey protein isolate for that task. Ultra-filtered isolates deliver high leucine, near-zero carbs, and lightning-fast absorption. That’s why athletes call it the best protein powder for weight loss.
Casein Protein
Casein, on the other hand, is not soluble in water and is digested more slowly than whey-when ingested, it forms a clotted gel in the stomach that provides a sustained slow release of amino acids into the bloodstream over several hours. Due to casein’s slower rate of absorption, it is often touted on health blogs as being useful for weight loss because it could hypothetically promote fullness, especially if ingested before periods of fasting, such as before bed. However, multiple studies have found no clear evidence that casein is more effective than any other protein source for satiety or weight loss.
Soy Protein
Soy protein powder is derived from soybeans, and unlike many plant-based proteins, it contains adequate levels of all essential amino acids. It is a common alternative to milk protein for vegans or people with dairy sensitivities or allergies. Soy protein is absorbed fairly rapidly by the body, although it is not as bioavailable as animal-based proteins.
Pea Protein
Pea protein powder is made from yellow split peas, and can be an option for vegans or people with allergies or sensitivities to soy or dairy. Pea protein is rich in eight of the nine essential amino acids; it is low in methionine, which can be obtained from other sources including rice and animal proteins. There is limited research on the effects of pea protein.
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Other Supplements with Potential Benefits
Several natural supplements have been proven to help you burn more fat. These natural solutions include caffeine, green tea extract, soluble fiber supplements, and yohimbine.
- Caffeine: Caffeine is a substance commonly found in coffee, green tea, and cocoa beans. It’s also a popular ingredient in commercial fat-burning supplements - and for good reason. A 2021 review of studies suggests that the caffeine in coffee can prevent and reduce fat stores in the body. It can also boost your metabolism and help your body burn additional fat. A 2024 study found that caffeine can boost basal metabolic rates by increasing systemic catecholamine levels. Catecholamines are molecules that act as neurotransmitters and hormones; they include dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline). However, these health benefits are only temporary. Plus, it’s important to note that caffeine can interfere with quality sleep, which has negative effects on weight management. Many people experience side effects from caffeine such as a rise in blood pressure and heart rate, sleep problems, anxiety or jitteriness or gastrointestinal problems. In high doses, caffeine can cause vomiting, heart palpitations and seizures. People with high blood pressure or heart problems should check with their health care provider before taking a supplement with caffeine.
- Green Tea Extract: Green tea extract is simply a concentrated form of green tea. It provides all the benefits of green tea in a convenient powder or capsule form. In addition, these two compounds complement each other and can help you burn fat through a process called thermogenesis. In simple terms, thermogenesis is a process in which your body burns calories to produce heat. For instance, an analysis of six studies found that taking a combination of green tea extract and caffeine helped people burn 16% more fat than a placebo. In an earlier study, scientists compared the effects of a placebo, caffeine, and a combination of green tea extract and caffeine on burning fat. They discovered that the combination of green tea and caffeine burned roughly 65 more calories per day than caffeine alone and 80 more calories than the placebo. Studies have shown that while no detrimental effects have been reported from green tea itself, excess consumption may prove to be harmful to the liver, particularly if taken on an empty stomach. Experts warn that large doses could cause liver damage. Signs may include yellowing of the skin or eyes, nausea and stomach pain. Do not exceed the recommended dosage.
- Soluble Fiber: There are two different types of fiber: soluble and insoluble. Interestingly, studies have shown that soluble fiber can help you burn fat by curbing your appetite. In addition, soluble fiber helps slow down the delivery of nutrients to the gut. When this happens, your body takes more time to digest and absorb nutrients, which can leave you feeling full for longer. What’s more, soluble fiber may also help you burn fat by reducing how many calories you absorb from food. While you can get all the soluble fiber you need from food, many people find this challenging. If that’s the case for you, try taking a soluble fiber supplement such as glucomannan or psyllium husk.
- Yohimbine: Yohimbine is a substance found in the bark of Pausinystalia yohimbe, a tree found in Central and Western Africa. It’s commonly used as an aphrodisiac, but it also has properties that may help you burn fat. Yohimbine works by blocking receptors called alpha-2 adrenergic receptors. These receptors normally bind adrenaline to suppress its effects, one of which is encouraging the body to burn fat for fuel. Since yohimbine blocks these receptors, it can prolong adrenaline’s effects and promote the breakdown of fat for fuel. Because yohimbine keeps your adrenaline levels elevated, it may cause side effects like: nausea, anxiety, panic attacks, high blood pressure. Yohimbe can also interact with common medications for blood pressure and depression. If you take medications for these conditions or have anxiety, you might want to avoid yohimbine. More clinical research is needed on yohimbine before it can be recommended as a go-to fat-burning supplement.
- Probiotics: Probiotics are beneficial bacteria that live in your gut and help break down and digest food. One 2018 review of 15 well-designed trials found that probiotics, either in foods or in supplements, helped overweight and obese people reduce their body weight and body fat. Some manufacturers are combining probiotics with prebiotics, a type of fiber that feeds gut bacteria. Although few studies have examined the safety of probiotics, they have a long history of safety, particularly in healthy people, according to the NIH. If you have a weakened immune system, rare side effects may occur from taking probiotics.
- Berberine: Early research also indicates berberine could help with weight loss. GI symptoms such as nausea, diarrhea, bloating, and constipation. Berberine may also interact with prescription medications.
Safety and Regulation: A Critical Eye
Commercial fat-burning supplements are widely available and very easy to access. However, they often do not live up to their hefty claims and may even harm your health. That’s because fat-burning supplements do not need to be approved by the Food and Drug Administration before they can be sold on the market. Instead, it’s the manufacturer’s responsibility to ensure that their supplements are tested for safety and effectiveness. And many fat-burning supplements have been pulled off the market because they were tainted with harmful ingredients. There have even been cases in which contaminated supplements caused dangerous side effects like high blood pressure, strokes, seizures, and even death. Remember that a supplement cannot replace health-promoting activities like exercising and eating a balanced, nutrient-rich diet. Talk with a doctor if you’re interested in developing a healthy program that can help you manage your weight.
The Importance of a Holistic Approach
It is important to understand that these studies have been conducted with Olympic and competition athletes, and thus the average individual who exercises recreationally should consult with a doctor before using caffeine as a supplement.
Supplements need to be accompanied by changes to diet and lifestyle. “If your diet and lifestyle isn’t going to be conducive to losing fat, fix that first,” he says. A supplement cannot replace health-promoting activities like exercising and eating a balanced, nutrient-rich diet.