Best Weight Loss Tip

Fiber For Losing Weight While Pregnancy

Fiber is an indigestible form of carbohydrate including polysaccharides, oligosaccharides, lignin, and other plant components. The human body lacks the enzymes to digest the components in fiber, but it is far from an inert substance. Dietary fibers are often classified as soluble and insoluble. Soluble fiber dissolves in water, thus attracting water and forming a gel, and slows digestion, creating a feeling of fullness. Food sources of soluble fiber include apples, blueberries, oats, nuts, and beans. Insoluble fiber can have a laxative effect and adds bulk to fecal matter, helping to prevent constipation. Whole wheat and other whole grains, cruciferous vegetables like broccoli and cauliflower, dark leafy greens, and grapes are all sources of insoluble fiber. Getting adequate fiber in the diet is associated with overall health benefits, though foods that have “added” fiber such as chicory root or psyllium are not known to have the same health benefits as foods with naturally occurring fiber. These foods may also cause gastrointestinal (GI) distress in some individuals. Thus, it is best to educate athletes on obtaining fiber from natural foods including fruits, vegetables, whole grains, and legumes.

Glycemic Index

Carbohydrates can also be classified according to the body’s glycemic response to carbohydrate-containing foods. That is, glycemic index is the rise in blood glucose level over baseline over a 2-hour period following consumption of a specified amount of carbohydrate (usually 50 g). This is then compared to the blood glucose response to the same amount of a reference food (usually either glucose or white bread). A numerical value is assigned to this food and allows comparison of various carbohydrate foods and how they impact blood glucose levels. Because we typically do not consume foods in isolation, using the glycemic index is not usually practical and has obvious limitations. The concept of glycemic load has been established to factor in both quantity and quality of the carbohydrate in question. Glycemic load equals the grams of carbohydrate in a serving of a food times the glycemic index. For example, watermelon has a high glycemic index, though contains few grams of carbohydrate per serving. Thus, the effect of this high glycemic index food on blood glucose might not be as great as a food with a high glycemic index and has more grams of carbohydrate per serving. However, what is not accounted for here is the effect of other nutrients of other foods that are eaten at the same meal. Consuming protein-containing food along with a high glycemic index food will mitigate the effect on blood glucose.

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Use of the glycemic index and glycemic load as a way to characterize the quality of carbohydrates is controversial. There lacks standardization of how glycemic index values are tested and measured, as well as variability of the glycemic index in the foods themselves (including relation to where they were grown, how they were processed, and cooking methods). There is variability between individuals’ blood glucose response to a given food; this is just to name a few of the concerns with using glycemic index or load as a measure of carbohydrate quality. Regardless, research has demonstrated the damaging role elevated blood glucose levels have on the development of chronic diseases, including obesity and diabetes. There are considerable health implications for understanding glycemic index and glycemic load that are outside of the scope of this text. As it pertains to exercise, glycemic index has limited application for athletes and the timing of nutrient intake as we will see in the following section on carbohydrate recommendations.

Carbohydrate Metabolism

When individuals consume carbohydrate-containing foods, the carbohydrate portion is digested via enzymatic action and is ultimately released as glucose in the blood. The pancreas senses increased levels of glucose in the blood and releases insulin to promote the cellular uptake of glucose to meet immediate energy needs while maintaining homeostatic balance of glucose in the blood (between 70 and 110 mg/dL). The remaining glucose gets stored. Through glycogenesis, glucose gets stored with water as glycogen as a stored form of energy, though the amount that can be stored is limited. Most glycogen is stored in the muscle (about 300 to 400 g), while some amount is also stored in the liver to help regulate blood glucose (70 to 100 g). These amounts can be altered slightly through training and dietary manipulation, as will be discussed in Chapter 6 on carbohydrate loading. Any remaining glucose will get stored as fat in adipose tissue via lipogenesis.

Carbohydrate’s Role in Exercise

Carbohydrate is a primary source of energy, and the fact that glycogen is stored right in the muscle supports the importance of carbohydrate as a quick and efficient energy source for muscular contraction and movement. In fact, athletes can think of their muscles as having little gas tanks right inside of them. Just as one would not drive a car with an empty tank of gas, an athlete should be encouraged to think of “topping off” their gas tanks before exercise with carbohydrate foods and possibly during exercise as well. Aerobic exercise relies upon muscle glycogen to support ATP production. Think back to Figure 3.4 illustrating carbohydrate’s contribution to energy production relative to exercise intensity. At low to moderate intensity, carbohydrate is contributing less energy relative to fat; however, it is still an important energy provider. The longer the exercise duration, the more likely carbohydrates stores especially coming from muscle glycogen become depleted. As exercise intensity increases, there is a greater reliance upon carbohydrate as an energy source. At high-intensity exercise, whether intermittent or short duration, carbohydrate is required to supply energy. Without sufficient carbohydrate availability, athletes experience increased fatigue and exercise duration or intensity or both becomes limited. Athletes want to ensure their “gas tanks” are full as they head into a training session.

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