Understanding Human Nutrition and Metabolism
What is Nutrition?
Nutrition is the process by which cells incorporate elements and perform nutritional functions. Cells are grouped in the following way: cells associate to form organs, organs coordinate to form systems, and systems cooperate to allow your body to function, think, work, and play.
Metabolism: A Series of Chemical Reactions
Metabolism includes anabolism (building tissues like muscle, bone, and blood) and catabolism (breaking down substances and tissues).
Food provides fuel for these chemical reactions. During rest, you need energy to maintain vital functions such as breathing, heartbeat, and blood circulation.
The basal metabolic rate (BMR) is defined as the amount of energy used when the body is at rest, supporting cellular processes and the manufacture and repair of tissues.
Food must be digested in the gut to be converted, absorbed, and utilized in metabolic reactions.
Calories: Measuring Energy in Food
The energy contained in food is measured in calories. A calorie is the amount of heat needed to raise the temperature of one gram of water by one degree Celsius. A kilocalorie (kcal) corresponds to 1000 calories.
Foods contain different energy values. The essential nutrients are proteins, lipids, carbohydrates, vitamins, minerals, and water.
Formulas:
- Proteins: x4
- Carbohydrates: x4
- Lipids: x9
Feeding vs. Nutrition
Feeding is the voluntary act of providing and ingesting food.
Nutrition is the set of physiological processes by which the body receives, processes, and uses the chemicals in food.
Diet relies on cultural and economic factors, while nutrition determines how we improve our bodily processes.
What are Nutrients?
The human body needs a continuous supply of materials that we ingest. These nutrients, which must be present in the diet, are:
- Lipids
- Carbohydrates
- Proteins
- Minerals
- Vitamins
- Water
These nutrients provide energy to boost metabolism and cellular activities. They also provide chemical building blocks, such as amino acids, to build complex molecules. Minerals and vitamins are involved in various metabolic reactions, and water is essential for nutrient transport.
Cells use energy to maintain their complexity and perform specific functions. The three nutrients that provide energy are fats, carbohydrates, and proteins.
Dietary Recommendations
- Increase consumption of fruits, vegetables, and whole grains.
- Reduce consumption of refined sugar.
- Reduce fat intake, and prioritize unsaturated fats.
- Reduce consumption of animal fat (choose lean meat, poultry, and fish).
- Reduce salt intake and foods high in sodium.
- Reduce foods high in cholesterol.
What is Basal Metabolic Rate (BMR)?
BMR is the energy required to maintain life processes, the minimum energy needed to stay alive.
Measurement of BMR
- 12-hour fast
- Resting, lying down
- Neutral thermal environment
Factors Affecting Metabolic Rate
- Body weight
- Lean tissue mass and fat
- External body surface
- Skin type
- Acclimatization to external temperature
Children have a very high BMR, the elderly have a low BMR, women have a lower BMR than men, and men have a medium BMR.
During stress, hormonal activity increases the metabolic rate.
A pregnant woman should add 285 kcal/day, and a breastfeeding mother should increase her caloric intake by 500 kcal/day.
Calculating Ideal Weight
Ideal weight corresponds to the number of kilograms a person should weigh according to their height, sex, and age. The World Health Organization (WHO) uses body mass index (BMI) as a way to determine ideal weight.
Body Mass Index (BMI)
BMI indicates a person’s nutritional status considering two factors: weight and height.
Formula: BMI = current weight / height2
- Underweight: < 20
- Normal: 20 – 24.9
- Overweight: 25 – 27.8 (men), 25 – 27.3 (women)
- Obesity: > 27.8 (men), > 27.3 (women)
Diet Definition
A diet is a group of substances we eat normally that allows us to maintain an adequate state of health.
Proper Diet
A proper diet provides adequate energy, allows for the maintenance or achievement of ideal weight, and provides all necessary vitamins and minerals.
Balanced Diet
A balanced diet provides:
- Sufficient energy nutrients
- Sufficient plastic nutrients and regulatory functions (proteins, minerals, and vitamins) in balanced amounts
Balanced amounts:
- Protein: 15%
- Carbohydrates: 55-60%
- Lipids: 30%
Carbohydrate Metabolism
Carbohydrates are converted into glucose and absorbed by the intestine. They pass to the liver, where they are converted into glycogen, an energy reserve substance used when glucose is not available.
As needed, glycogen is converted back into glucose and enters the blood. Muscle glycogen is used during recurrent, intense muscle activity.
Glycogen is stored in the liver (up to 100g) and in some muscles (up to 200g). Excess blood glucose is converted into fat and accumulates in adipose tissue as long-term energy storage.