Week 3 Nutrition

Fiber Overview

Carb that can't be digested by the human body and does not provide significant kcalories Related terms are soluble (present in fruits, oats, barley, rye, legumes, avocados), insoluble (always the dominant type of fiber naturally occurring in foods. All high fiber foods are good sources of insoluble fiber), dietary (non digestible CHO and lignin that occur naturally and intact in plants), functional (non digestible CHO added to foods with beneficial physiological effects that are extracted from plants or animals, or synthesized), and total (dietary + functional). Fibers can be added to processed foods to thicken and reduce fat and calories Its presence affects GI function, Intestinal microbiota, the amount of intestinal gas, and nutrient absorption

Hoe Fiber Affects GI Function

Increases the weight of material in the lumen of the intestine Producing a larger, softer stool, which promotes healthy bowel function Prevent constipation Reduces transit time

Physiological Functions of Fiber

Intake inversely correlated with heart disease (reducing cholesterol absorption with soluble fiber), weight control, diabetes, cancer Improves laxation Lowers high total and LDL cholesterol Maintenance of normal LDL cholesterol Attenuation of blood glucose response Fermentation by colonic microbiota

Oligosaccharides

Mostly undigested seeds and beans

Fiber in the Digestive Tract

Some fibers such as cellulose and oligosaccharides are not digested because human enzymes cannot break the bonds that hold their subunits together. For instance, heating makes potato starch more digestible, but cooling the cooked potato reduces the starch's digestibility. Fiber increases the weight of material in the lumen of the intestine. The extra weight is due to the bulk of the fiber itself, the water held by the fiber, and the increase in the number of bacteria.16 The result is a larger, softer stool, which promotes healthy bowel function by stimulating peristalsis. More peristalsis causes the muscles of the colon to work more, become stronger, and function better, helping to ease evacuation of the stool and prevent constipation. When fermentable fibers reach the colon, they are broken down by the bacteria that reside there. This produces short-chain fatty acids, which serve as a fuel source for cells in the colon and are absorbed into the bloodstream where they provide energy to other body cells and may play a role in regulating cellular processes. These short-chain fatty acids also make the colonic contents more acidic, which inhibits the growth of undesirable bacteria and favors the growth of beneficial species of bacteria, such as Lactobacilli and Bifidobacteria, that are well adapted to acid conditions. Anyone who has ever eaten beans knows of their potentially embarrassing side effect of flatulence. Beans cause gas because they are particularly high in the oligosaccharides raffinose and stachyose, which cannot be digested by enzymes in the human stomach and small intestine. Intestinal gas is also a by-product of the bacterial fermentation of other fibers. The amount of gas produced depends on the type of fiber and the amount consumed. Constipation can also be a problem if fiber intake is increased without an increase in fluid intake. Fiber binds certain minerals, preventing their absorption. The added bulk provided by fiber slows overall nutrient absorption, in part by slowing stomach emptying. This is beneficial for people who are trying to lose weight because they may feel satiated after fewer calories are consumed.27 However, a high-fiber diet may be a disadvantage for people with a small stomach capacity because they may satisfy their hunger before their nutrient requirements are met. Once in the small intestine, fiber slows nutrient digestion and absorption because it increases the volume of the intestinal contents and absorbs water, forming viscous solutions. This speeds passage through the GI tract, reduces contact between digestive enzymes and food, and decreases the amount of contact between nutrients and the absorptive surface of the small intestine, all of which slow the absorption of glucose and other nutrients (Figure 4.12).

The Intestinal Microbiota

The right mix of microorganisms in the intestinal microbiota is important for optimal gastrointestinal function, maintenance of immune function, and for overall health. The bacteria act on unabsorbed portions of food and on substances secreted by the GI tract, such as mucus, to produce nutrients that the bacteria themselves can use and that can affect the health of the host body. Bacterial breakdown of undigested carbohydrates produces small fatty acids referred to as short-chain fatty acids. The presence of the microbiota and the substances it produces help maintain the mucosal layer that lines the intestine and serves as a barrier, modulate the amount of inflammation in the gut, and prevent the growth of disease-causing bacteria. The gut microbiota is also important for the maturation of the immune system, because it allows the immune system to tolerate harmless bacteria and respond to harmful ones. A healthy microbiota is diverse and resists change under physiological stress, inhibiting the growth of harmful bacteria. Patients with inflammatory bowel disease, irritable bowel syndrome, and colon cancer have been found to have increased levels of harmful bacteria and reduced levels of healthy ones. Adults with obesity, type 2 diabetes, and atherosclerosis have been found to have alterations in the composition of the gut microbiota when compared to healthy controls Fibers that serve as a food supply for beneficial bacteria are called prebiotics. A diet high in prebiotics promotes the maintenance of a healthy microbiota. Prebiotics are found naturally in certain foods and are sold as dietary supplements. Another option for maintaining a healthy intestinal microbiota is the consumption of live beneficial bacteria, referred to as probiotics.1 When these living bacteria, such as the Lactobacillus in yogurt, are consumed in adequate amounts, they live temporarily in the colon, where they inhibit the growth of harmful bacteria and confer other health benefits on the host. The bacteria must be consumed frequently because they are flushed out in the feces. Data suggest that probiotic therapy can be helpful for the prevention and treatment of antibiotic-induced diarrhea, acute infectious diarrhea, and persistent diarrhea in children.

Fructose Metabolism

To the liver, you get an increase in acetyl-CoA which leads to more fat More lactate production makes a more acidic environment