Carbohydrates Aren't Enemies If to Know How to Eat Them
In Western society we generally eat between 200 and 320 grams of carbohydrate daily. Unlike fat, carbohydrate metabolism is rather rapid. Bread, rice, potatoes, fruit, vegetables and sugar are all classified as carbohydrates.
Carbohydrates are broken down to form glucose. Glucose is of vital importance to 3 major organs: the brain, heart and nervous system. In a typical day, these organs can use about 130 to 180 grams of carbs. Carbohydrates, once broken down to form glucose, get stored in the body as glycogen. Each gram of glycogen is bound to 3-4g of water. About 70g of glycogen is stored in your liver and another 300-400g is stored inside muscle cells.
The total carbohydrate stores of the body can be depleted within a single exercise session. Having adequate glycogen stores prior to exercise then is important as low carbohydrate levels are directly related to increases in muscle breakdown. This is because the body can make glucose it needs from muscle tissue. This process of making glucose from protein is called gluconeogenesis.
What happens to a bowl of pasta once it has been eaten?
Although popular diet books have convinced people that eating a bowl of pasta, (which contains carbohydrates) is converted to fat, comprehensive medical evidence does not support this conclusion. In a recent study in the American Journal of Clinical Nutrition 2003, scientists analysed what happens to 75 grams of carbohydrate, the equivalent of about two small bowls of pasta. Of the 75 grams, 32 grams of carbohydrate was converted to and stored as glycogen. The body used the remaining carbohydrate as energy. Not one single gram was converted to fat.
People often get confused between eating sensibly (one medium sized bowl of pasta with a low fat sauce), and over consuming (possibly 2-3 large bowls of pasta with cream based sauce). Foods such as whole grain bread, rice and pasta also contain an important and healthy substance called resistant starch. As its name suggests resistant starch, escapes digestion in the small intestine, and is broken down in the large intesnine where it can be protective against cardiovascular disease, diabetes and obesity. Studies also show that people, who consume diets rich in unrefined carbohydrates, without overeating, have lower rates of obesity, heart disease, diabetes, and some cancers. Carbohydrates are important to our diet, especially if you are active.
Can carbohydrates get converted to fat?
One of the first, and most intriguing studies involving massive carbohydrate meals was conducted by Dr Kevin Acheson. This study consisted of overeating bread, jam and drinking fruit juice, adding up to 479 grams of carbohydrate. To put this into perspective this is about the same amount of food as 1.4 — 1.5 kg of cooked pasta, or 7 medium bowls of pasta. You and I could never eat so much food. The amount fat that was made from carbohydrate was between 0 to 1.8 grams only.
In a second study by Dr Acheson, 500 grams of carbohydrate were fed to young healthy lean people, the amount of fat stored from carbohydrate was a mere 9 grams. This process of converting carbohydrate to fat is termed 'de novo lipogenesis', and does occur in humans, but the conversion of carbohydrate to fat is small. This article is not for one moment suggesting that it's OK to eat 500 grams of carbohydrate because it's not! In fact to eat so much food for even moderately active people is plain ridiculous. In a society where overeating and large portion sizes are the norm, we need to cut down on carbohydrate consumption, yet realise that a medium size bowl of pasta, a couple of slices of bread, with plenty of fresh fruit and vegetables eaten daily, fit the model of healthy eating.
Carbohydrates and Energy Dalance
In western society we eat fats, protein and carbohydrates together. There is no single study to date that accurately describes what happens to the human body when fed large amounts of fats, protein and carbohydrates together. When 150 grams of fat and 110 grams of protein are added to 320 grams of carbohydrates (approximate macronutrient intakes) then our daily energy intake skyrockets to about 3100 calories, 44% and 100% greater than what an average man and woman expend in a typical inactive day (an inactive man burns about 2150calories and an inactive woman 1550 calories each day).
Do carbohydrates convert to fat if eaten after 6pm?
Many people advocate that it's best not to eat starch-containing carbohydrates at night (such as potatoes, bread, rice or pasta). Does the human body convert carbohydrates to fat if you eat them after 6pm? In fact there are many carbohydrate curfew times such as 12, 2, 4 and 6pm, and its origins have been elusive yet widely practiced. People who advocate such eating protocols claim that by eliminating starch-containing carbohydrates such as bread, rice, pasta, and potatoes, from their meals and eating more vegetables, salads and meat, you can lose weight. The supposed reason for this is that carbohydrates don't get used at the end of the day because people are less active. The claim is that the pasta you eat at night gets converted to fat. Let's have a look at this concept!
I have searched nearly 200 medical journals, personally spoken to some of the world's most prominent scientists about this topic, and unfortunately there is not one scrap of medical evidence to back such claims. As the title of this article reads, 'Carbohydrates cannot tell the time', so starch-containing carbohydrates don't get converted to fat after 6pm! In a very recent issue of the American Journal of Clinical Nutrition, a diet that consisted of eating less bread, no rice and more lean meat, had no weight loss advantages over a diet that contained bread, rice, and was lower in lean meat. Both groups lost about 8kg in about 12 weeks, when they reduced the amount of food they ate from about 2024 calories to 1430 calories.
A medium sized bowl of pasta containing about 50 grams of carbohydrate eaten at any time of the day or night gets converted to glycogen, not fat. Although we may be physically less active at the end of the day, our brain, nervous system and heart still require glucose to function optimally, and can use 50-60 grams of carbohydrate while we sleep. Once again no one is suggesting eating as much pasta as you want either, as we know people are eating more food than ever before. Eating vegetables and salad at night is very health giving, but in reality this is not a new message, and is what health authorities have been advocating people eat for years. In Italy where pasta is served daily, and some Asian countries where rice is on the menu each night, these meals are served in small to medium sizes, and accompanied by large amounts of salads and/or vegetables. Other carbohydrate curfew theories suggest that we should only eat low Glycemic Index carbohydrates at night (low GI carbohydrates contain very little starch).
Further to this, does cutting carbohydrates out mean that you have a free licence to eat as much cheese, chocolate, fat, alcohol and protein food as you like? A little common sense should surely prevail here. A better eating protocol would be to eat less food after 6pm, especially if you are inactive! It is important to make the clear distinction between popularity and credibility of these types of diets, as popularity is not credibility.
Carbohydrates, Insulin and Weight Gain
When carbohydrates are eaten, metabolised and released as glucose in the blood stream, insulin is released. Insulin transports the glucose to the muscle and liver cells where glucose is stored as glycogen. Insulin doesn't convert carbohydrate to fat! It does however result in transporting some fat already in the blood stream into fat cells. Does this mean that carbohydrates indirectly make us fat? Does it also mean that we need to cut out carbohydrates, which will then mean we will release less insulin, and hence burn more fat? The simple answer is no!
Scientists have known since the 1960's that, like carbohydrates, protein foods such as meat, chicken and fish, also produce insulin. In a landmark study in 1997, Dr Susan Holt of the University of Sydney in Australia published a paper in the American Journal of Clinical Nutrition clearly describing how lean beef, and fish produced more insulin than white pasta, when served in equal amounts. This is because protein too needs insulin to help transport it muscle and liver cells. So anytime we eat carbohydrates or protein we produce insulin. Insulin doesn't make us fat. Popular low-carbohydrate diet books suggested the 'insulin-fat storing' relationship, and hence suggested people eat large amounts of protein, have either not kept up with recent research or have little understanding or simple human physiology. Protein also stimulates large amounts of insulin!
Low sugar, low fat or both?
In western society we consume far too much sugar, and possibly far too much carbohydrate based foods. A recent study in the American Journal of Public Health showed that when we eat pasta when dining out, pasta meals are over 180% greater in portion size than what health authorities recommend. A 500ml soft drink (55grams of sugar) and a 250 grams chocolate bar (140grams sugar), can be 'passively' consumed throughout the day, especially by today's inactive youth, adding up to about 70 teaspoons of sugar. Very few scientific studies however show that eating large amounts of sugar, or carbohydrates, alone cause obesity. This is because in western society we eat carbohydrates, fats and proteins, never just carbohydrates. In a world where we tend to almost overeat when we can, carbohydrates play a role with obesity, as part of the bigger picture, which also include:
- Large portion size of food,
- Increased consumption of food consumed away from home, from takeaway, restaurants, snacks,
- Large amounts of extra energy we eat,
- Our massive fat consumption,
- Alcohol consumption,
- Low fibre consumption,
- Dramatic declines in physical activity.
The message to cut down on sugar seems to be having some effect, with sugar consumption in the US falling by 3% for the first time in history, however we have a long way to go. In response to the low-sugar message that is currently sweeping the world, people have mistakenly abandoned the low-fat message. The focus is now on reducing sugar and carbohydrates, yet it seems we have forgot all about the studies on fat and its close relationship with weight gain obesity and disease. Rather than separating the two we should be intelligently putting the 'low-fat message', and the `low sugar/reduction in carbohydrate' message together, instead of abandoning one for the other! This would make complete sense as we would then be eating less fat containing foods, less sugar and carbohydrate based foods and hence less energy.
In the US, at the same time that sugar consumption declined, fat consumption increased 6% and there is 150 grams of fat available for each person per day. Unfortunately in response to the 'low-fat message was wrong' theme, food manufacturers have astoundingly produced products that contain 1/3 extra fat in the US.
Conclusion
A diet high in carbohydrates, and low in fat that has been recommended by health professionals, does not mean eating massive amounts of carbohydrate as people have interpreted. It doesn't mean eating large amounts of sugar, nor does it encourage overeating. It means a large percentage of carbohydrates (-50%) as part of a diet that is lower in energy, and contains large amounts of fibre found in fruit, vegetables, cereals and grains, along with adequate protein, and low amounts of fat (especially animal fat).
The key message here is to reduce sugar and carbohydrate consumption as part of a healthy diet that also reduces fat, protein, and alcohol. Put simply we eat too much food. Eating sensible amounts of carbohydrate doesn't cause fat gain, but overeating carbohydrates and remaining inactive can certainly contribute!
