ugg boots for women sale Getting the most out of food
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When we consume a food or drink, the nutrients contained are released from the matrix, absorbed into the bloodstream and transported to their respective target tissues. However, not all nutrients can be utilised to the same extent. In other words, they differ in their bioavailability. pregnancy) are among the internal factors. Because aspects such as nutrient status also determine whether and how much of a nutrient is actually used, stored or excreted, some definitions of bioavailability restrict themselves to the fraction of a nutrient that is absorbed.3
The bioavailability of macronutrients carbohydrates, proteins, fats is usually very high at more than 90% of the amount ingested. flavonoids, carotenoids) can vary widely in the extent they are absorbed and utilised. Therefore, the following sections will use micronutrients and phytochemicals as examples to illustrate the different stages at which nutrient bioavailability can be influenced.
Effects of food matrix and chemical form of nutrients
The first step in making a nutrient bioavailable is to liberate it from the food matrix and turn it into a chemical form that can bind to and enter the gut cells or pass between them. Collectively this is referred to as bioaccessibility.4 Nutrients are rendered bioaccessible by the processes of chewing (mastication) and initial enzymatic digestion of the food in the mouth, mixing with acid and further enzymes in the gastric juice upon swallowing, and finally release into the small intestine, the major site of nutrient absorption. Here, yet more enzymes, supplied by the pancreatic juice, continue breaking down the food matrix.
In addition to the bodily means of mastication and enzyme action, the digestibility of food matrices, especially of plant foods, is aided by cooking or pureeing the food. For example, whereas raw carrots and spinach are good sources of dietary fibre, cooking them allows the human body to also extract a much larger fraction of the carotenoids contained.5
Minerals and other nutrients exist in different chemical forms in the food and this can influence their bioavailability. A classic example is iron. In general we talk about two types of dietary iron; haem and non haem iron. The former is only found in meat, fish and poultry, whereas the latter occurs in foods of plant and animal origin. Haem iron mainly stems from the haemoglobin and myoglobin molecules responsible for oxygen transport and storage in the blood and muscles, respectively. Once released from the food matrix, the haem molecule acts like a protective ring around the central iron atom. Thus, it shields the iron from interaction with other food components, keeps it soluble in the intestine, and is absorbed intact through a specific transport system on the surface of the gut cells.6 In contrast, non haem iron is poorly soluble under intestinal conditions and easily affected by other components of the diet.2 Therefore only a small fraction is taken up by the cells.
Sometimes vitamins and minerals are added to foods to increase their nutritional value a process called fortification. In the case of the B vitamin folic acid, which is often added to breakfast cereals, flour and certain spreads, this added folic acid usually is more bioavailable than that naturally present in the food, commonly referred to as dietary folate. Enhancers can act in different ways such as keeping a nutrient soluble or protecting it from interaction with inhibitors. For example, since carotenoids are fat soluble, adding small quantities of fat or oil to the meal (3 5 g per meal) improves their bioavailability.9 Similarly, meat, fish and poultry, while containing highly bioavailable iron themselves, are also known to enhance the absorption of iron from all foods. Although this ‚meat factor‘ has yet to be identified, an influence of the muscle protein has been suggested.10
Vitamin C is also a strong ‚helper‘, being able to increase iron absorption by two or three times.11 This means, for example, having a glass of orange juice with a bowl of breakfast cereal helps the body use more of the iron in the cereal.