9.1 Introduction to Metabolism and Nutrition
Chapter Objectives
After studying this chapter, you will be able to:
- Describe the processes involved in anabolic and catabolic reactions
- List and describe the steps necessary for carbohydrate, lipid, and protein metabolism
- Explain the processes that regulate glucose levels during the absorptive and postabsorptive states
- Explain how metabolism is essential to maintaining body temperature (thermoregulation)
- Summarize the importance of vitamins and minerals in the diet
Introduction
Eating is essential to life. Many of us look to eating as not only a necessity, but also a pleasure. Louisiana cuisine is world-famous, and Louisianans’ love affair with food comes from the unique blend of cultures each contributing its own culinary traditions. Food is often the centerpiece of many Louisiana family gatherings and social events.
You may have been told since childhood to start the day with a good breakfast to give you the energy to get through most of the day. You most likely have heard about the importance of a balanced diet, with plenty of fruits and vegetables. But what does this all mean to your body and the physiological processes it carries out each day? You need to absorb a range of nutrients so that your cells have the building blocks for metabolic processes that release the energy for the cells to carry out their daily jobs, to manufacture new proteins, cells, and body parts, and to recycle materials in the cell.
This chapter will take you through some of the chemical reactions essential to life, the sum of which is referred to as metabolism. The focus of these discussions will be anabolic reactions and catabolic reactions. You will examine the various chemical reactions that are important to sustain life, including why you must have oxygen, how mitochondria transfer energy, and the importance of certain “metabolic” hormones and vitamins.
Metabolism varies, depending on age, sex, activity level, fuel consumption, and lean body mass. Your own metabolic rate fluctuates throughout life. By modifying your diet and exercise regimen, you can increase both lean body mass and metabolic rate. Factors affecting metabolism also play important roles in controlling muscle mass. Aging is known to decrease the metabolic rate by as much as 5 percent per year. Additionally, because males tend to have more lean muscle mass than females, their basal metabolic rate (metabolic rate at rest) is higher; therefore, males tend to burn more calories than females do. Lastly, an individual’s inherent metabolic rate is a function of the proteins and enzymes derived from their genetic background. Thus, your genes play a big role in your metabolism. Nonetheless, each person’s body engages in the same overall metabolic processes.
Louisiana Lagniappe
Louisiana is known for its unique cuisine, with crawfish as a standout favorite. Crawfish boils are not just a chance to indulge in this delicious Cajun classic, but create opportunities to connect with family and friends (Figure 9.2). You may be wondering if crawfish are good for you? Crawfish can be a nutritious addition to a balanced diet, but their healthiness depends on how they are prepared and consumed.
According to the Louisiana Department of Health, crawfish are a nutritional, low-fat seafood. One serving of crawfish (about 5/8 cup of crawfish tails) contains a healthy portion of Vitamin A, Calcium, Iron, as well as Vitamin B12, selenium, zinc, and iron, which support overall health (Figure 9.3).
Crawfish are high in protein and low in total fat, including unhealthy saturated fat and trans-fat, making them a good option for muscle building and repair. They are relatively low in calories compared to other protein sources. Crawfish are well within the 300-milligram daily limit of cholesterol recommended by the American Heart Association and the National Academy of Sciences. Additional foods like potatoes, corn, mushrooms, and sausage, are usually added to the boil, making it a balanced meal.
Is there a downside to eating boiled crawfish? It depends on how they are prepared, and how much you eat. The term “crawfish boil” actually refers to the bags of seasoning or liquid that are used to cook the crawfish, and they are loaded with sodium- up to 1,000 milligrams per serving. The Centers for Disease Control and Prevention recommends that Americans consume less than 2,300 milligrams of sodium per day. The amount drops to 1,500 milligrams of sodium per day if you have high blood pressure, or other heart-related issues. For a healthy person, this means a single serving of boiled crawfish can contain over half of your daily recommended intake of sodium. If you have high blood pressure, you will nearly meet your entire daily sodium intake in a single meal. It’s also easy to overeat at crawfish boils, since the crawfish are usually served on a tray, or laid out on a table. You don’t have a plate to rely on portion size.
To reduce sodium intake, choose low-sodium seasoning blends for your boils and avoid adding extra salt during cooking. Stay hydrated by drinking plenty of water, and limit alcoholic beverages, as they can contribute to dehydration, which may be exacerbated by high sodium levels.