32 Chapter 2: Basic Nutrition Fad Diet Examples Low-carbohydrate diet (e.g., Adkins / Keto / Carnivore). As the name suggests, these diets promote either severely restricting or eliminating carbohydrate intake. As previously mentioned, although seemingly effective, the weight loss associated with these diets is primarily a result of a temporary decrease in water weight due to reduced carbohydrate intake. When carbohydrate intake is significantly reduced, glycogen stores in the muscle are depleted, which results in weight loss due to reduced water retention. However, once carbohydrates are reintroduced, the muscles begin to store water again resulting in weight gain. Additionally, since most foods contain at least some carbohydrates, some of the weight loss associated with these diets is a result of an overall reduction in the number of calories consumed per day. It is important to note that carbohydrates are the body’s preferred source of energy. When inadequate amounts of carbohydrates are consumed, the body produces ketones (chemical produced by the body when fats are broken down for energy) as an alternative energy source. However, burning of ketones instead of carbohydrates, leads to decreased mental and physical performance. Figure 2.1 shows the impact that various diets (i.e., high-carbohydrate intake, normal carbohydrate intake, and low-carbohydrate/high-fat intake) can have on muscle glycogen levels and exercise duration (Balsom et al., 1999). Some of the common side effects reported with a keto diet include: excessive thirst, frequent urination, fatigue, hunger, confusion, anxiety, irritability, tachycardia, lightheadedness, sweating and chills. Additionally, prolonged use of a keto diet can also lead to a condition called ketoacidosis, which can be fatal. Figure 2.1. Correlation between Muscle Glycogen Content and Exercise Duration Intermittent fasting. Intermittent fasting is not as much a diet as it is a particular pattern of eating. Some of the more common types of intermittent fasting include: 16:8 (i.e., 16-hour fast with 8-hour eating window); 20:4 (i.e., 20-hour fast with 4-hour eating window); 5:2 (i.e., 5 days no restrictive with 2-days of fasting); 24-hour fast; 36-hour fast; alternate day fasting; and
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