In-Depth Look at Carbohydrates

Everything you need to know about carbohydrates including carb types, GI, digestion, fiber, glucose and relationship with fat storage and physical activity.

Carbohydrates are the human body’s key source of energy, providing 4 calories of energy per gram. When carbohydrates are broken down by the body, the sugar glucose is produced; glucose is critical to help maintain tissue protein, metabolize fat, and fuel the central nervous system. There are different types of carbohydrates, simple and complex carbohydrates, to understand carbohydrates we need to look a bit into the science on the subject.

TYPES OF CARBOHYDRATES

Carbohydrate pasta fatSimple Carbohydrates:

Monosaccharides: which include Glucose, (also called dextrose) Fructose (also called levulose, or fruit sugar) and Galactose.

Disaccharides: which include Sucrose, Lactose, and Maltose

Simple carbohydrates or sugars may cause a fast rise in blood sugar, thereby stimulating excess insulin production, which causes a fast drop in blood sugar. Glucose and Maltose have the highest glycemic effect.

Complex Carbohydrates:

Oligosaccharides: (Partially digestible polysaccharides) Include Maltodextrins, Fructo-oligosaccharides, Raffinose, Stachyose, and Verbascose. These partially digestible polysaccharides are commonly found in legumes and while they may cause gas and bloating, are considered healthy carbohydrates. They are less sweet than mono- or disaccharides. Raffinose, stachyose, and fructo-oligosaccharides are found only in small amounts in certain pulses, grains, and vegetables.

Polysaccharides: (Digestible Polysaccharide and Indigestible polysaccharides). Digestible polysaccharides; include Amylose, Amylopectin, Glucose polymers. These complex carbohydrates should provide the main source of carbohydrate energy. Glucose polymers are made from starch and are often used in sports drinks and athlete gels.

Indigestible polysaccharides: these complex carbohydrates provide fiber, which is important for gastrointestinal tract health and disease resistance.

Other Complex Carbohydrates: These include Mannitol, Sorbitol, Xlyitol, Glycogen, Ribose. Mannitol, sorbitol, and Xlyitol (sugar alcohols) are nutritive sweeteners that do not produce tooth decay, they are commonly used in products because of their moisture retention and food-stabilising characteristics, but they are digested slowly and are known to cause gastrointestinal distress if consumed in high amounts. Glycogen is the main carbohydrate storage form in animals, while ribose is part of the genetic code.

DIGESTION AND ABSORPTION OF CARBOHYDRATES

To obtain glucose from our newly-eaten food, the digestive system must first render the starch and disaccharides from the food into monosaccharides that can be absorbed through the cells lining the small intestine. The largest of the digestible carbohydrate molecules, starch, requires the most extensive breakdown. Disaccharides, on the other hand, must be split only once before they can be absorbed.

Fibre, starch, monosaccharides and disaccharides enter the intestine. (Some of the starch is partially broken down by an enzyme from the salivary glands before it reaches the small intestine). An enzyme from the pancreas digests the starch to disaccharides. Enzymes on the surface of the intestinal wall cells split disaccharides to monosaccharides. Monosaccharides enter capillary, then are delivered to the liver via the portal vein. The liver converts Galactose and fructose to glucose.

STORING GLUCOSE AS GLYCOGEN

After we have eaten a meal blood glucose rises, the pancreas is the first organ to respond. It releases the hormone insulin, which signals the body’s tissues to take up surplus glucose. From some of this excess glucose, muscle and liver cells build the polysaccharide glycogen. The muscles hoard two thirds of the body’s total glycogen and use it just for themselves during exercise. The liver stores the other third and is more generous with its glycogen; it makes it available as blood glucose for the brain or other organs when the supply runs low. When the blood glucose concentration drops and cells need energy, a pancreatic hormone, glucagons, floods the bloodstream. Thousands of enzymes within the liver cells release a surge of glucose into the blood for use by all the other body cells. Another hormone, epinephrine, does the same thing as part of the body’s defence mechanism in times of danger (the fight or flight theory).

Although glucose can be converted into body fat, body fat can never be converted into glucose to feed the brain adequately. This is one reason why fasting and low-carbohydrate diets are dangerous. When there is a severe carbohydrate deficit the body has two problems. Having no glucose, it has to turn to protein to make some, thus diverting protein from vitally important functions of its own such as maintaining the body’s immune defences. Proteins functions in the body are so indispensable that carbohydrate should be kept available precisely to prevent the use of protein for energy; this is called the protein-sparing action of carbohydrate. Also without sufficient carbohydrate the body cannot use its fat in the normal way. (Carbohydrate has to combine with fat fragments before they can be used for energy). The minimum amount of carbohydrate needed to ensure complete sparing of protein and avoidance of ketosis is around 100 grams a day in an average sized person. This has to be digestible carbohydrate and considerably more (three or four times more) than this minimum is recommended.

GLYCOGEN AND ITS IMPORTANCE TO PHYSICAL ACTIVITY

 Glycogen is stored with water, in the ratio 1 gram of carbohydrates to 3 grams of water. During exercise, this glycogen is broken down into glucose, which, along with fat, supplies the muscle with energy. In short bursts of high intensity (anaerobic) exercise, such as sprinting and weight lifting, a large amount of energy is quickly required. Glycogen is the main fuel as only it can be converted fast enough. Very little fat is used. In longer periods of low intensity exercise (aerobic) such as cycling, swimming, long distance running, glycogen is the main fuel but as these stores are used up, a greater proportion of fat is used. Fat cannot be broken down quickly enough to continually meet high energy expenditure. Therefore, the ability to perform prolonged exercise is related to your body's glycogen stores. Fatigue is an indication of low levels of glycogen in the exercising muscles. A high level of glycogen at the start of exercise can delay fatigue from taking place early. So, the amount of carbohydrate we eat determines the amount of glycogen stored, which in turn greatly affects our performance level. When we eat foods like fruit, cereal or bread, glucose goes into our bloodstream quickly, ready to provide immediate energy to the brain, muscles or other body tissues demanding energy. If you eat a low carbohydrate diet, it is less efficient for our bodies to store glycogen in your body. We may especially notice an energy drain if we do not take days off from our workouts routine. A glycogen drain will make us may feel listless and uninterested in exercising. You need to take a few days off from your work out to allow your body to recharge the glycogen stores. Glycogen stores are built up by the consumption of plenty of carbohydrate foods. Good sources of carbohydrates are bananas, bread, cereals, potatoes, rice, and pasta. Choosing whole meal varieties of these foods will also increase dietary fibre. Muscle glycogen must be replaced after training; otherwise you will not be able to train to your maximum at your next session. It can take up to 48 hours for muscle glycogen stores to be replenished. If your diet is low in carbohydrate, it will take even longer to do that. Therefore, it is also recommended that you should vary heavy and light training sessions to allow muscles to refuel properly.

In short, carbohydrates efficiently replace the glycogen stores in the muscles and liver. Glycogen is necessary for muscle contraction. If we do not eat enough carbohydrate or get enough rest, the level of glycogen steadily declines, leaving us fatigued and unable to perform effectively.

CONVERTING GLUCOSE TO FAT

When we are hungry we tend to overeat. After meeting the needs of the body cells, energy needs and filling glycogen stores, the body then takes another path to handling incoming carbohydrates, by using the liver to break the extra glucose into small fragments and puts them together into a more permanent energy storage compound called FAT, (this would happen with excess protein and fat as well) The fats are then released into the blood stream, carried to the fatty tissues of the body and deposited there. Unlike liver cells which can store four to six hours of glycogen, the fat cells can store an unlimited quantity of fat. Even though excess carbohydrate is converted to fat and stored, a balanced diet, high in complex carbohydrates helps control body weight and lean tissue. Carbohydrate food contributes less to body fatness then do the normal high fat foods.

GLYCEMIC EFFECT

The glycemic effect is when some foods elevate our blood glucose and insulin concentrations higher than other foods. Scientists measure the glycemic effect of food by administering a food or meal and then observing how fast and how high the blood glucose rises and how quickly the body responds by bringing the blood glucose levels back to normal. Most people can quickly adjust, but people with abnormal carbohydrate metabolism may experience extreme blood glucose levels. These people would do well to choose foods with a low glycemic effect such as brown rice, whole grain breads and pasta’s, sweet potatoes, some vegetables especially green vegetables, and some fruit’s. Many factors work together to determine a food’s glycemic effect and the result is not always as expected. Ice cream, for example, produces less of a response then potatoes; baked potatoes produce less of a response than mashed; a sweet, juicy apple produces a low response; dried beans of all kinds are known for keeping blood glucose remarkably steady. Importantly, a food’s glycemic effect differs when it is eaten alone or as part of a mixed meal. The foods mixed in meals tend to balance each other with regard to glycemic index. Most people eat a variety of foods in a meal and so need not to worry about the glycemic index of the foods they choose. Most peoples systems control their blood glucose perfectly, regardless of the glycemic index ratings of the food they consume.

Glycemic Food Index Table:

Glycemic Index of Fruit Glycemic Index of Pasta Glycemic Index of Breads inc. Muffins & Cakes
Apple 38
Banana 55
Cantaloupe 65
Cherries 22
Grapefruit 25
Grapes 46
Kiwi 52
Mango 55
Orange 44
Papaya 58
Pear 38
Pineapple 66
Plum 39
Watermelon 103
Spaghetti 43
Ravioli (meat) 39
Fettuccini (egg) 32
Spiral Pasta 43
Capellini 45
Linguine 46
Macaroni 47
Rice vermicelli 58
Bagel 72
Blueberry Muffin 59
Croissant 67
Donut 76
Pita Bread 57
Pumpernickel Bread 51
Rye Bread 76
Sour Dough Bread 52
Sponge Cake 46
Stone Ground Whole wheat bread 53
Waffles 76
White Bread 70
Whole Wheat Bread 69
Glycemic Index of Vegetables Glycemic Index of Snacks Glycemic Index of Cookies
Beets 69
Broccoli 10
Cabbage 10
Carrots 49
Corn 55
Green Peas 48
Lettuce 10
Mushrooms 10
Onions 10
Parsnips 97
Potato (baked) 93
Potato (mashed, instant) 86
Potato (new) 62
Potato (french fries) 75
Red Peppers 10
Pumpkin 75
Sweet Potato 54
Cashews 22
Chocolate Bar 49
Corn Chips 72
Jelly Beans 80
Peanuts 14
Popcorn 55
Potato Chips 55
Pretzels 83
Snickers Bar 41
Walnuts 15
Graham Crackers 74
Kavli Crispbread 71
Melba Toast 70
Oatmeal Cookies 55
Rice Cakes 82
Rice Crackers 91
Ryvita Crispbread 69
Soda Crackers 74
Shortbread Cookies 64
Stoned Wheat Thins 67
Vanilla Wafers
Water crackers 78
Glycemic Index of Beans Glycemic Index of Dairy Glycemic Index of Sugars
Baked Beans 48
Broad Beans 79
Cannellini Beans 31
Garbanzo Beans (Chickpeas) 33
Lentils 30
Lima Beans 32
Navy Beans 38
Pinto Beans 39
Red Kidney Beans 27
Soy Beans 18
White Beans 31
Milk (whole) 22
Milk (skimmed) 32
Milk (chocolate flavored) 34
Ice Cream (whole) 61
Ice cream (low-fat) 50
Yogurt (low-fat) 33
Fructose 23
Glucose 100
Honey 58
Lactose 46
Maltose 105
Sucrose 65
Glycemic Index of Grains Glycemic Index of Cereals  
Buckwheat 54
Bulgur 48
Basmati Rice 58
Brown Rice 55
Long grain White Rice 56
Short grain White Rice 72
Uncle Ben's Converted 44
Noodles (instant) 46
Taco Shells 68
Kellogg's All Bran 51
Kellogg's Bran Buds 45
Kellogg's Cornflakes 84
Kellogg's Rice Krispies 82
Kellogg's Special K 54
Oatmeal 49
Shredded Wheat 67
Quaker Puffed Wheat 67
 

GOOD SOURCES OF CARBOHYDRATES

Carbohydrates are an essential part of our diet. They provide most of the energy for the body, as well as many vitamins and nutrients. They are found in abundance in many plant foods such as rice, pasta, beans, potatoes and many other grain products and vegetables.

When selecting grain products, people are urged to select whole grain foods such as whole-wheat bread, brown rice, whole-grain pasta, quinoa, whole oats, and bulgur.

Complex carbohydrate sources:

Vegetables Legumes Grains* Fruits Beet Carrots Corn Peas Potatoes Turnips Kidney-beans Lentils Lima beans Pinto beans Split peas Barley Oats Rice Rye Wheat Edible seeds.

*Also in grain products such as whole wheat bread, crackers or pasta.

Simple Carbohydrate Sources (Natural)

Fructose (fruit sugar)
Lactose (milk sugar)

Fruits and juices such as apples, oranges, pineapples Dairy products such as milk and yogurt.

CARBOHYDRATES AND PHYSICAL ACTIVITY

Physical activity dramatically increases the rate of energy expenditure, any athlete no matter what type of training he/she does must strategise in order to best supply the needed energy to achieve success in their sport. It is critical for any athlete to obtain sufficient total energy intake to support total energy requirements, including those for normal tissue maintenance, growth, tissue repair, and the energy requirements of the activity itself. Virtually all surveys that have been conducted with athletes have concluded that they fail to consume sufficient energy to fully satisfy their needs. Think of it this way you are planning to drive your car on a hundred mile trip, you go to the petrol station to fuel up but only put enough petrol in the car for eighty miles, the car just won’t get there, and poorly fueled athletes will also have difficulties doing what is required to be competitive. It is generally accepted that athletes should consume sufficient carbohydrate to meet the majority of their exercise-related energy needs, plus enough carbohydrates to restore muscle glycogen stores between exercise sessions.

Ideally athletes should consume complex carbohydrates whenever possible, but should consume simple carbohydrates during and immediately after exercise. Other energy substrates (protein and fats) should also be consumed to fulfill total nutrient requirements, but carbohydrate should remain your predominant energy source. It is difficult for athletes to take in sufficient energy and carbohydrate unless there is a well-established plan to do so. You should remember that training alone, without a sound nutritional planning to support your training.

CARBOHYDRATE REQUIREMENTS

The recommendations for carbohydrates are:

  1. Every day eat 5 – 9 servings of a combination of vegetables and fruits.
  2. Every day eat 6 – 11 servings of a combination of breads, cereals, starches, legumes, and other complex carbohydrates.
  3. Use sugar sparingly from refined sugars and no more than 10% of total daily calories.

Daily Carbohydrate Intake Recommendations:

Group Carbohydrates
Sedentary men and non pregnant womem At least 55% of energy intake, assuming energy intake is adequate
Male and non-pregnant female recreational athletes At least 60% of total energy intake, assuming energy intake is adequate
Endurance-trained athletes 6-10 grams per kilogram of body weight
Strength trained athletes 6-10 grams per kilogram of body weight

If you want to know the number of grams of carbohydrates you should eat daily, look to the nutrition facts panel on the food label on the foods that you buy. The math is already calculated for you! According to the label, when consuming 2,000 calories daily, your carbohydrates should come in at 300 grams. If your daily intake is more like 2,500 calories, then increase to 375 grams. Both will put your carbohydrate intake at 60 percent of your total calories.

So now you know all about Carbohydrates are next question is how many grams of carbohydrates do we need? We already know that we require between 40% and 60% of total calories as carbohydrates so from the table below you can see how many you require.

The table below gives the amount of carbohydrates required in grams for different bodyweights and different percentages of total calories for someone who is moderately active.

Bodyweight (lbs) Total Calories 40% of total calories 50% of total calories 60% of total calories
140lb 2604cal 260 grams 326 grams 396 grams
150lb 2790cal 279 grams 348 grams 419 grams
160lb 2976cal 298 grams 372 grams 446 grams
170lb 3162cal 316 grams 395 grams 474 grams
180lb 3348cal 335 grams 418 grams 502 grams
190lb 3534cal 353 grams 442 grams 530 grams
200lb 3720cal 372 grams 465 grams 558 grams

FIBER

 Fibre is important for our health and well being. Among health-related benefits are that it helps to maintain bowel regularity and reduce serum cholesterol levels, and improve the ratio of “good” and “bad” cholesterol. Fibre is found in carbohydrate foods especially unrefined grains, fruits, and vegetables and when choosing high-fibre foods in hope of receiving some of the benefits you would be wise to seek out a variety of fibre sources, wheat bran, which is composed mostly of insoluble fibres, is one of the most effective stool-softening fibre, but oat bran with more soluble fibre, has more of a cholesterol-lowering effect. The fibre of legumes, oats, apples, and carrots may also lower blood cholesterol. To consumers this means that although a food may play a star role in providing one type of fibre, to receive the whole range of fibre benefits one must choose a variety of whole foods each day. Like any other substances, if taken in excess, fibre can cause harm. Fibre carry’s water out of the body and can cause dehydration. Most iron is absorbed at the beginning of the intestinal tract, and excess insoluble fibre, by speeding up the transit of foods through the digestive system, may limit irons absorption. Binders in some fibre act as chelating agents and link chemically with nutrient minerals (iron, zinc, calcium, and others). Then carry them out of the body. Some fibre interferes with the body’s use of carotene to make vitamin A. too much bulk in the diet can limit the total amount of food consumed and cause deficiencies of both nutrients and energy. The malnourished, the elderly, and children who consume no animal products are especially vulnerable to this chain of events.

Fibre intake should exceed 20 grams per 1000 calories consumed, and the diet should contain a minimum of 30 grams per day.

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