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dietary management - fundamentals

There are three main nutrients that provide energy to our bodies, namely PROTEIN, CARBOHYDRATE and FAT. Food consists of a combination of these nutrients. Some foods are also rich sources of VITAMINS and MINERALS. Vitamins and minerals are termed ‘micronutrients’ because we only require them in tiny amounts. They have a number of functions and are vital to good health, but they do not contribute any energy to the diet.

Your body requires energy for growth, muscular activity and basic body functions. If you eat an excessive amount of energy, your body will store that which it does not use as extra body fat. In order to lose weight, you are required to take in less energy (by eating less, or absorbing fewer calories, as one does after a gastric bypass), and to use up more calories each day (by being more physically active). Different foods all provide different amounts of energy depending on how much protein, carbohydrate and fat they provide. Energy can be measured in either kilojoules (kJ - metric) or calories (kcal - imperial).

Protein is essential for building, maintaining and repairing tissue. Although the body can manufacture its own protein, there are certain protein components that can only be obtained through the diet. The quality of different proteins varies: some proteins are of a higher quality as they provide all the protein components and are thus termed ‘complete’ proteins. Good sources of protein include foods such as meat, poultry, fish, seafood, milk, eggs, cheese, yoghurt, peanut butter, nuts, dried beans and peas (split peas) and lentils. It can be difficult to maintain an adequate intake of protein after a gastric bypass, but it is essential that you get enough: protein deficiency can cause hair loss, fatigue, weaken your immune system and aggravate anaemia.

The main function of carbohydrates in your diet is to provide energy: the trick is to eat enough to provide you with enough energy, but not to overeat – remember that excess energy is stored as body fat. The main carbohydrate sources in the diet are sugars and starches. Sugars are generally very quickly and easily absorbed from the gut, while starches take a little longer as they require more digestion. Starches are "complex" carbohydrate sources, which also contribute other nutrients such as fibre (roughage), essential vitamins (especially vitamin B complex) and minerals, while sugar provides only energy.

a) Sugar
Sugar (any type) in the diet provides energy in the form of refined carbohydrate, but little else! Sugar can also cause dumping syndrome after a gastric bypass, so it is wiser to rather choose complex carbohydrates which will also provide you with other nutrients. Foods high in sugar include: sugar (all types - white, brown, castor, icing), jam, marmalade, honey, syrup, sweets, chocolates, treacle, condensed milk, puddings, ice cream, cool drinks, sweet biscuits and cakes.

b) Starches
Starches such as breads and cereals, rice, pasta and potatoes are all complex carbohydrate sources. Although your intake of starch will be low after a gastric bypass, you will need some in order to keep your blood glucose levels stable, and provide a source of fibre. Fibre has been shown to have many favourable roles such as cancer prevention, increased satiety (feeling of fullness), lowering cholesterol and blood glucose, preventing constipation and maintaining gut health. Unrefined complex carbohydrates included foods such as: wholewheat bread, bran cereals, brown rice, potato with the skin, oats, barley, samp, beans and mealies.

Fat is a concentrated source of calories, and too much fat in the diet can therefore easily lead to weight gain, since a high fat diet will substantially increase your energy intake. Besides this, a high dietary fat intake has also been linked to diseases such as heart disease and cancer. After a bypass, fat can cause dumping syndrome.

Although the amount of fat one eats is important, the type of fat is also very significant. For example, saturated fat (mainly animal fat sources) has been found to raise blood cholesterol, while unsaturated fat can help lower cholesterol provided it is taken in the correct amounts. As with protein there are certain fats (essential fatty acids) that cannot be manufactured by the body and must therefore be consumed in the diet. These fats are found predominantly in plant oils and oily fish (salmon, mackerel, pilchards etc). Sources of unsaturated fat include: oil (all types), margarine, avocados, olives, nuts and seeds. Saturated fats are found in butter, lard, cream, mayonnaise, meat and chicken (mainly in the skin), egg yolk, full cream dairy products and cheeses.

Although vitamins and minerals do not contribute any energy to the diet and occur in much smaller amounts in foods, they are essential for survival as they perform vital functions in the body. They are scattered throughout different foods, but are found in particularly high amounts in fruit and vegetables. You require extra vitamins and minerals after surgery as you will not only eating far less food, but will also absorb fewer nutrients, and will require life-long vitamin and mineral supplementation.

An adequate fluid intake is very important, especially during physical activity, in hot weather and when consuming a high fibre diet. Fibre in the gut absorbs water, and water is required to hydrate the fibre and soften stools. Low fluid intakes can lead to constipation. You should try to consume 6-8 glasses of fluid a day. The best fluid is water; but you may also include diluted fruit juices and cordials, tea and rooibos tea. Try to have at least half your daily fluid as plain water: add a slice of lemon or orange, or a sprig of mint, to add flavour. Have small sips at a time, and do not drink with meals.

In simple terms, whether or not weight is lost or gained is determined by the following equation:
i.e. Food and drink = basal metabolism + physical activity

  • If your energy input is greater than your output, you will gain weight, as your body will store this excess energy as fat.
  • If your energy input is less than your output, you will lose weight as your body compensates for this loss of energy, and uses up body fat for energy.
  • If your energy input is equal to your energy output, you will maintain your weight.

Gastric bypass helps to cause weight loss in a number of ways:

  • It reduces the size of the stomach and therefore reduces the amount of food that can be eaten at a time. The capacity of your new stomach pouch is initially as small as 20 – 30ml (about 2 Tblsp), but expands with time to eventually accommodate about 125ml (½ cup).
  • You will feel full far sooner, after eating far less food. This makes it easier to follow your new eating plan.
  • Part of the intestine has been bypassed. As the small intestine is the place where food is digested and absorbed, this results in malabsorption. Your body will therefore not be able to absorb all the nutrients and calories from your food.