Fundamentals of Nutrients and the History of Nutrition скачать в хорошем качестве

Fundamentals of Nutrients and the History of Nutrition

In order to survive, the human organism needs to take in oxygen, food and water. We can survive only about three minutes without air, three days without water and three weeks without food. Because food is so important to our survival, it’s been studied extensively. And since 1827, when a British physician by the name of William Prout first proposed that humans need three macronutrients to survive, physicians, scientists and, increasingly the general public, have been trying to figure out exactly how much of each of .these nutrients will optimize our health. But, to some extent, the focus on nutrients rather than food has confused many people. Michael Pollan: and we tend to get lost in this conversation about nutrients, good and bad. And it's understandable because scientists need to reduce things to a single variable to study them, and the variable in food would appear to be the nutrient, and so we have lots of studies. But we also have lots of studies that show that simply removing or boosting nutrients or turning them into supplements doesn't seem to work, that food is much more complicated, it's a system. A basic understanding of the nutrients can provide a helpful background for our discussions about food, so we’ll briefly review the nutrients and how our bodies use them. But, for the most part, this course will focus on discussions about food . Because, ultimately, we eat food, not nutrients. Dietary carbohydrates are combinations of sugar units that come in both simple and complex forms. Simple carbohydrates include the monosaccharides, or single-sugar units, like glucose and fructose as well as the disaccharides, or two-sugar units, like sucrose or table sugar. Complex carbohydrates (or polysaccharides) include the dietary starches that our body can breakdown and digest, and also the indigestible polysaccharides that make up dietary fiber. During the process of digestion, carbohydrates are broken down and converted to glucose, which can then be metabolized by the body to produce useable energy in the form of ATP. If energy demands are low, glucose can be stored and most of the time it’s stored as adipose tissue. Dietary proteins are broken down into their component parts, amino acids, during the process of digestion and these amino acids can be used to build and repair lean tissues in the body and perform many other important functions, but amino acids can also be broken down and used for energy and, if they are consumed in excess, they can contribute to fat stores in the body as well. Dietary fats can also be broken down into smaller components and used for energy or they can be stored as adipose tissue depending on our energy needs. Fats are the most energy dense storage form, providing 9 Cal of energy for every gram. In contrast, carbohydrates and proteins provide only Cal of energy per gram and alcohol provides 7 Cal per gram. This is one of the reasons we’ve evolved to store excess nutrients as adipose tissue. And this brings us to the underlying physiologic cause of overweight and obesity. Any calories that aren’t converted into useable energy (ATP), are stored in the body for later use. Most of the time, they’re stored as adipose tissue. So, disturbing the energy balance, to favor energy expenditure over energy storage should be one of the first priorities for people who are struggling to lose excess weight. This can be achieved by consuming fewer calories, burning more calories through exercise, or a combination of both. In addition, when long-term health is the end goal, the quality of the food our patients eat matters just as much as the number of calories they consume. Within each category of macronutrient, we need to help our patients choose foods that will support their health rather than working against it. Course by Maya Adam, MD Directed by William Bottini Animated by Huy Tran & William Bottini Editing by William Bottini & Tamsin Orion Special thanks to Michael Pollan, Tracy Rydel, and David Eisenberg