A review of some of the most popular diet programs reveals that they fall along a continuum from "anti-carbohydrate” to "anti-fat." The Standard American Diet (SAD) is typically comprised of 43-50% carbs. Low carbohydrate diets have been a popular trend for many trying to lose weight, as well as athletes seeking to improve performance. Diets focused on minimizing carbs, such as Atkins, South Beach and The Zone, recommend eating anywhere between 10% and 40% of calories from carbohydrates.
On the other side of the coin, Ornish and Pritikin recommend consuming upwards of 60% of calories from carbohydrates while limiting fat intake, claiming that this is the healthiest way to prevent and/or manage chronic diseases, such as heart disease. (Riley, 1999)
As you can see, there is a wide range of recommendations, which can be confusing, to say the least. Here we will shed some light on carbohydrates, enabling you to make an informed decision about the optimum percentage of carbohydrate intake for your health, weight management and performance.
Carbohydrates can be classified as:
- Monosaccharides: e.g., glucose, galactose and fructose
- Oligosaccharides: e.g., sucrose (table sugar), maltose (alcohol) and lactose (milk sugar)
- Polysaccharides: e.g., cellulose, glycogen, starch and pectin
Glucose (aka blood sugar) is the primary form in which carbohydrates are transported in the body. It is easily broken down and:
- Used to supply energy
- Stored as glycogen in the muscles or liver
- Converted to triglycerides and stored as fat
Fructose is found in fruit and honey. It is the sweetest monosaccharide and is eventually converted to glucose. The worldwide consumption of sucrose and fructose has risen exponentially since the 1800s. There are a number of concerns about the health hazards of high fructose corn syrup-sweetened beverages, including soft drinks and fruit drinks, and the fructose they provide, including higher energy intake, risk of obesity, risk of diabetes, risk of cardiovascular disease, risk of gout in men, and risk of metabolic syndrome. This is one form of carbohydrate that definitely warrants avoiding. (Bray, 2010)
Polysaccharides are considered complex carbohydrates and can come from plants or animals. Starch is the storage form of carbohydrates in plants and can exist as amylose or amylopectin, which are found in grains, pasta, cereal, beans, potatoes and rice. The amylopectin found in these foods affects the digestibility, glycemic index (GI) and metabolic response.
The glycemic index describes how a food, meal, or diet affects blood sugar during the postprandial (after a meal) period. There is evidence that diets consisting of low glycemic carbohydrates may be useful in preventing obesity, heart disease, colon and breast cancer, and type II diabetes, based on their effects on blood glucose and limited insulin response. (Pawlak, 2004)
Glycogen is the primary animal polysaccharide. It is stored in skeletal muscles and the liver, is the primary source of energy during most forms of exercise, and can be a major determinant of performance and recovery. (Antonio et al., 2008)
Carbohydrates are metabolized through three different pathways:
- Glycolysis (anaerobic)
- Glycogenolyis (anaerobic)
- Oxidative (aerobic)
The pathway utilized is determined by the intensity and duration of an activity. The initial energy for short-term, high-intensity bouts of exercise depends on the phosphagen system and fast glycolysis. Short-term activities requiring greater power outputs depend on anaerobic energy, whereas longer duration activities with less power outputs shift to aerobic energy. As exercise intensity declines, there is a metabolic shift from carbohydrate to fat for energy. (Antonio et al., 2008)
Carbohydrate Considerations in Exercise
Inadequate carbohydrate consumption can result in the inability to restore muscle glycogen and consequently, be ergolytic (adversely affect performance), as well as disruptive to exercise adaptations. Over time, this can contribute to overtraining. (Antonio et al., 2008)
Carbohydrate recommendations for anaerobic athletes (e.g. weight lifting, bodybuilding, sprinting, soccer, football, basketball)
A low carbohydrate diet (<42%) in this population will adversely affect exercise adaptations and performance. Athletes who perform high intensity exercise do best on a diet that is 55-60% carbohydrate (6-10 g/kg/day) depending on the intensity, volume and duration of training. This maximizes storage of muscle glycogen. Ideally, 45% of the carbohydrates should be low glycemic and the balance, moderate to high glycemic (1-2 hours after exercise). (Antonio et al., 2008)
Carbohydrate recommendations for aerobic athletes (e.g. marathon, cross-country skiing, triathlon, >60 minutes)
The general recommendation for aerobic athletes is to consume more than 55% of calories from carbohydrates. This figure should be manipulated based on volume, duration and intensity, with a range from 5-12 g/kg/day. As with anaerobic athletes, high glycemic carbohydrates should be limited to 1-2 hours after exercise and only if other sources are unavailable. (Antonio et al., 2008)
Carbohydrate availability is optimum when consumed in the hours or days prior to the session, during exercise, and refueling during recovery between sessions. This is important for the competition setting or for high-intensity training where optimal performance is desired. Carbohydrate intake during exercise should be scaled according to the characteristics of the event. During sustained high-intensity sports lasting about an hour, small amounts of carbohydrate, including mouth-rinsing, enhance performance via central nervous system effects. While 30-60 g per hour is an appropriate target for sports of longer duration, events >2.5 hours may benefit from higher intakes of up to 90 g per hour. (Burke et. al, 2011)
The above recommendations should be fine-tuned with individual considerations based on total energy needs, specific training needs, feedback from training performance and carbohydrate tolerance. Carbohydrate-rich foods with a moderate to high glycemic index provide a readily available source of carbohydrate for muscle glycogen synthesis, and should be the major carbohydrate choices in recovery meals. (Burke et al. 2004) (Hawley and Burke, 1998)
Adequate carbohydrate consumption is essential for maintaining optimum glycogen stores, which affects performance and recovery and can help mitigate conditions that can lead to overtraining.
Carbohydrates and body composition
Physique athletes can periodize their macronutrients in order to maximize growth and then as they get closer to their event, lose fat while sparing lean body mass. This can be accomplished by eating as mentioned above in the weeks leading up to an event (anaerobic athletes). As the event gets closer, start tapering the training intensity, while at the same time replacing carbohydrates (especially high glycemic/refined carbohydrates) with fat and protein.
Volek et al. (2002), found that a carbohydrate-restricted diet resulted in a significant reduction in fat mass and a concomitant increase in lean body mass in normal-weight men, which may be partially mediated by the reduction in circulating insulin concentrations. (Volek et al. 2002)
So are carbohydrates bad?
Carbohydrates provide energy. Depending on one’s level of activity and goals, this macronutrient can be manipulated along with fats and proteins in order to optimize performance and/or body composition.
Because refined carbohydrates can have an adverse glycemic response, which over time can have a negative impact on health, they should be minimized or restricted to immediately post exercise and then generally avoided for the aforementioned reasons.
Examples of Low Glycemic Carbohydrates
Starch - sweet potatoes, squash, plantains, turnip, pumpkin, jicama
Non-starch - dark green leafy vegetables, other colorful, non-starchy vegetables (not corn or potatoes)
When it comes to fruit, berries, cherries, apples and grapefruit are good choices.
Antonio J, Kalman D, Stout J, Greenwood M, Willoughby D, Haff G. (2008). Essentials of Sports Nutrition and Supplements. New Jersey. Humana Press.
Bray G. Fructose: Pure, White, and Deadly? Fructose, by Any other Name, is a Health Hazard. J Diabetes Sci Technol July 2010 vol. 4 no. 4 1003-1007.
Hawley JA and Burke LM. (1998). Peak Performance: Training and Nutritional Strategies for Sport. Sydney: Allen and Unwin.
Burke LM, Kiens B, Ivy JL. Carbohydrates and fat for training and recovery. J Sports Sci. 2004 Jan; 22(1):15-30.
Burke LM, Hawley JA, Wong SH, Jeukendrup AE. Carbohydrates for training and competition. J Sports Sci. 2011; 29 Suppl 1:S17-27.
Pawlak DB, Kushner JA, Ludwig DS. Effects of dietary glycaemic index on adiposity, glucose homoeostasis, and plasma lipids in animals. Lancet. 2004 Aug 28-Sep 3; 364(9436):778-85.
Riley, R. Popular weight loss diets. Health and exercise implications. Clin Sports Med. 1999 JUl; 18(3):691-701.
Volek JS, Sharman MJ, Love DM, Avery NG, Gómez AL, Scheett TP, Kraemer WJ. Body composition and hormonal responses to a carbohydrate-restricted diet. Metabolism. 2002 Jul;51(7):864-70.