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Digestion & Metabolism

Digestion & MetabolismPart 1 : The Digestive System

The process of breaking down food into usable nutrients in known as digestion.

It takes place in the digestive system, a long, hollow tube that extends from the mouth through the entire body.

The digestive process starts before you even begin to eat the food.

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Just smelling and seeing food, or even thinking about it, can start saliva flowing in your mouth, which is the first of many digestive juices that act on food to break it down chemically.

Food is also broken down physically as your teeth grind it into tiny pieces.

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Chewing food is very important as it mixes the food with saliva, making it easier to swallow and digest.

Solid food should be chewed until it is the consistency of applesauce.

Once the food is swallowed, it passes into the esophagus, a long lube connecting the mouth to the stomach.

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The muscles of the esophagus contract and relax, creating a series of wave-like movements that force food into the stomach. This muscular action is called peristalsis.

The next stop on the digestive journey is the stomach, a muscular pouch on the left side of your body inside the rib cage.

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The walls of the stomach manufacture gastric juices, a combination of acids and enzymes that help in the chemical breakdown of food.

Additionally, the stomach also breaks down food physically through peristalsis.

The food is churned up until it becomes a thick, mushy liquid called chyme.

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Different kinds of food take different amounts of time to break down and leave the stomach.

Carbohydrates take the shortest amount of time, usually one to two hours.

Proteins take longer, usually three to five hours and fats take the longest, up to seven hours.

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That is why a food high in fat will keep you from feeling hungry for a longer time, while a meal high in carbohydrates can actually make you hungrier, or at least hungry more often.

From the stomach, chyme is released into the small intestine, a long winding tube about one-inch in diameter, a little at a time.

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Here, the chyme is acted upon by three digestive juices: (1) bial, a substance made in the liver, helps your body digest and absorb fats; (2) pancreatic juice, which contains enzymes that help break down carbohydrates, protein, and fats; and, (3) intestinal juice, which is produced in the small intestine and works with the other fluids to break down food.

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When fully broken down, carbohydrates turn into a simple sugar called glucose, the body’s basic fuel supply. Fats are changed into fatty acids and proteins are broken down into amino acids.

Vitamins, minerals, and water do not need to be broken down as they can be used by your body in the same form in which they occur in food.

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Once food has been broken down into nutrients, digestion is complete.

However, your body still needs to absorb the nutrients into the bloodstream and store them for later use.

Most absorption takes place in the small intestine …

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… which is arranged in folds and lined with tiny finger-like projections called villi, which increase the surface area of the intestine so that more nutrients can be absorbed.

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After nutrients are absorbed by the villi, they are carried through a blood vessel, called the portal vein to the liver.

One of the liver’s many jobs is to turn nutrients into forms the body can use.

Some nutrients, if not needed immediately, are stored for future use.

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Extra glucose, for example, is converted by the liver into glycogen, a storage form of glucose. If there is more glucose than can be stored, the rest is converted into body fat.

Fats are deposited throughout the body as an energy reserve.

Excess fatty acids and amino acids are also converted to body fat.

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Some nutrients, including most water-soluble vitamins are not stored for long.

If they are not needed, they are removed from the body with wastes.

After absorption, some waste material, including fibre, is left in the small intestine.

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This waste material is moved to the large intestine, also called the colon, which removes water, potassium, and sodium from the waste.

The remaining indigestible materials are stored as semi-solids in the rectum, or lower part of the large intestine, until eliminated.

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Metabolism & BMR

Metabolism & BMRHFA4M Food & Nutrition Sciences

Part 2: Basil Metabolic Rate & Daily

Caloric Needs

Metabolism is the chemical reactions in the body’s cells that converts fuel from food into the energy needed to do everything from moving to thinking and growing.

Metabolism refers to the number of calories your body burns for proper functioning (e.g., heart beating, stomach digesting, kidneys filtering, etc.)

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Some people are born with high metabolisms which means they have a hard time gaining weight. They can eat large amounts of food and do very little exercise, yet remain slim.

Others are born with a slow metabolism. They store more energy because their bodies don’t need as many calories to function properly. Any extra calories are stored as fat.

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Metabolism is in your genes but you can help to increase your metabolism by increasing your muscle mass.

Muscles are the “energy houses” in which calories are burned.

Those who have higher metabolisms have more muscle on their body and

thus require more calories for fuel.

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Basil Metabolic Rate (BMR) is the minimal amount of calories needed to sustain life in a resting individual.

This is the amount of energy your body would burn if you slept all day (24 hours) as it carried out our most basic functions.

Most of our daily energy expenditure is represented by about 60-70% by our

BMR.

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BMR calculations are average estimations and can change over time.

The following items can all have an effect on your BMR:

Age Body Composition Fever

Height Malnutrition Stress

Growth Starvation/Fasting

Temperature

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To calculate your personal Basil Metabolic Rate, follow the formula below. Remember to calculate the numbers in brackets first.

Women: BMR = 655 + (4.35 x weight in pounds) + (4.7 x height in inches) - ( 4.7 x age in years)

Men: BMR = 66 + (6.23 x weight in pounds) + (12.7 x height in inches) - ( 6.8 x age in years)

Calculate your BMRCalculate your BMR

Once you know your personal BMR, use the following equation to estimate your daily calorie needs should you want to maintain your current weight.

If you are sedentary (little or no exercise): Calories = BMR x 1.2

If you are lightly active (light exercise/sports 1-3 days/week): Calories = BMR x 1.375

If you are moderately active (moderate exercise/sports 3-5 days/week): Calories = BMR x 1.55

If you are very active (hard exercise/sports 6-7 days a week): Calories = BMR x 1.725

If you are extra active (very hard exercise/sports & physical job or 2x training): Calories = BMR x 1.9

Calculate your Daily Calorie NeedsCalculate your Daily Calorie Needs

If you want to gain body weight, you need to consume more calories than you burn.

One pound of body weight is roughly equivalent to 3500 calories, so eating an extra 500 calories per day will cause you to gain one pound a week.

Calorie Needs to GAIN WeightCalorie Needs to GAIN Weight

If you create a 3500-calorie deficit through diet, exercise or a combination of both, you will lose one pound of body weight.

The calorie deficit can be achieved either by calorie-restriction alone, or by a combination of fewer calories in (diet) and more calories out (exercise).

This combination of diet and exercise is best for lasting weight loss. Sustained weight loss is difficult or impossible without increased regular exercise.

Calorie Needs to LOSE WeightCalorie Needs to LOSE Weight

If you want to lose fat, a useful guideline for lowering your calorie intake is to reduce your calories by at least 500, but not more than 1000 below your maintenance level.

For people with only a small amount of weight to lose, 1000 calories will be too much of a deficit.

Calorie levels should never drop below 1200 calories per day for women or 1800 calories per day for men.

Reducing calories by 15-20% below your daily calorie maintenance needs is a useful and safe alternative rather than using standard amounts.

Just Remember … Just Remember …