This debate has raged for years. It is now time for an update by reviewing recent research, claims and some good old common sense. The arguments are summarised in terms of Pros and Cons.
When obesity develops in childhood, there is an increase in the number of fat cells, whereas in adults, the total amount of fat in each cell that increases. Decreasing the total energy (food calories) consumed or increasing the amount of energy burnt in exercise does change the number of fat cells present. Only the amount of fat in each cell can reduce. The process is slow and steady just as it was when weight was increased. Prevention of weight gain is far better than any treatment of obesity as it is hard to lose weight.
The potential energy derived from food is expressed in calories. The body can match energy intake and output in terms of calorie balance, but obese people often don't eat food to match their energy expenditure and food intake is often not related to energy needs. Many people eat for other reasons beside hunger- due to stress, boredom, eating food 'to feel good and happy', or eating through habit or for a reward?
Food consumption, both quality and quantity, are important for understanding why people are obese, and most overweight people will admit that they are excessive eaters or binge eaters. Most overweight people do not overeat all the time. Often they eat standard qualities and healthy foods most of the time but occasionally, or more one meal each day binge or eat too much. This is occurs commonly with women in caused by emotional stress, and less often in men. Sedentary lifestyles, inactivity and lack of exercise also contribute to weight increase, even when people are not overeating.
There are many stated causes of obesity with comprehensive arguments in favour and against each cause. Summaries for some of there causes are outlined below.
David Gillespie, a former lawyer in Australian, in his books Sweet Poison and The Sweet Poison Quit Plan, he claims that sugar (sucrose made up of glucose and fructose molecules) is the cause of the obesity epidemic because it is addictive and does not trigger a fullness reaction.He argues that the three major hormones insulin, leptin and cholecystokinin are not released when we eat sugar. He claims that 'fructose', which is in many fruits and other so called 'healthy foods' people eat as alternatives to refined sugar ate just as bad. He advocates diets that are very low in sugar, glucose and fructose. To him it is just common sense, but many people are falling into the trap of avoiding refined sugar, but replacing it with natural foods that are high in fructose - such as in kids lunches. The sugar-trap foods, that contain large amounts of sugar that people are unaware of are: Juice, sauces, pasta sauces, muesli and snack bars, breads, fruits - especially dried fruit.
David Gillespie recommends you eat only about 10 grams of fructose a day (= two pieces of fruit) , which is a major reduction from the 60 to 75 grams of fructose a day that most people eat.
The famous Food Pyramid dating from 1991, showcases various government recommendations on what you should eat to maintain a healthy weight. At the bases is a broad base of 6 to11 servings of food in the carbohydrate and grains group. The number of servings reduces as the pyramid narrows with smaller servings of fruit and vegetables and less again for dairy foods and meat. At the very apex of the pyramid are the fats and oils, which consumers should eat sparingly. The message from this is simply - reduce the proportion of dietary fat in your diet. This is related to the idea that fat as an energy store and that most of the dietary fat goes straight to the sores of body fat. Fat is much harder to metabolise during exercise for example, than carbohydrate and protein. The 'brick wall' that many marathon runners experience is often attributed to the exhaustion of glycogen and carbohydrates and the switch to less efficient fat metabolism. Likewise during starvation the body will break down carbohydrate and protein first and fat as a last resort.
The breakdown of fat in the intestine and absorption of fatty acids is much more complicated than for carbohydrates and proteins. This involves re-conversion of the fatty acids produced from the breakdown of fats and absorption through the lining of the gut, into triacylglycerols and lipoprotein complexes (chylomicrons). There particles are distributed through the blood and the connected lymph system for delivery to the various tissues for storage or production of energy through oxidation. The oxidation of fatty acids yields about 25% more energy per carbon atom than does the oxidation of carbohydrates, hence the value of fat as an energy reserve. So it would appear obvious that the more fat you eat the more will end up in your fat reserves. The issues here are:
Recent studies have clarified why eating less fat may help you lose weight. Surprisingly these studies suggest that it may not be the fat itself. Indeed the fat pyramid may be counter-productive as it shifts people to high-calorie low-fat foods such as bread and dairy products. It is the total energy intake, not fat itself, in relation to energy burnt through exercise determines body fat status. It is suggested that eating dietary fat increases body fat because the fat has a very high energy density. Dietary fat has a weak effect on your feeling of fullness. Eating dietary fat therefore tends to induce over-consumption of calories in a given portion of food.
From 1972 - 1990, Dr. Robert Atkins published several books about his low-carbohydrate diet, which lead to the 'low carb' craze at the start of the millennium. At one time it was suggested that as many as 15% of the American population was using a low-carbohydrate diet. There have been many clinical studies assessing the effectiveness and safety of these diets (both pro and con). Many researchers have raised concerns about the health hazards of the high-fat and high-protein diets produced when carbohydrates are eliminated and replaced with bacon, eggs, steak and other meat and dairy products. Users of the diet often lost weight quickly, but found it hard to make the transition to a maintenance diet to keep the weight off.
The principle for low-carbohydrate diets is to eliminate virtually all carbohydrates - including both starches and sugars, fruit, fruit juice, beans, rice, cereals, starchy vegetables, bread, pasta, cous cous and other grain products. In research study conducted by researchers at the University of Pennsylvania, most subjects lost weight during the first 6 months, but regained it during the next six months so that the net weight loss was similar to other diets. In a one-year clinical trial of 10 obese subjects, reported in JAMA in 2005, found that those on the Atkins diet lost 2.1 kg, while those on Weight Watchers lost 3 kg, Zone dieters lost 3.2 kg, and Ornish dieters lost 3.3 kg. Another study reviewed about 100 research studies on various low-carbohydrate, high-protein weight diets found that the weight loss was not due to the 'low carbs' but to the reduced calorie intake in the food eaten when carbohydrates were eliminated. Other reports have also found calorie reduction to be the most important factor in weight loss. There have been more recent studies that are more supportive and suggest that the high-protein may be less harmful, but the really long studies have not been completed.
For most people, obesity is generally thought to occur from eating too much and not exercising enough. Studies have shown that portion sizes continue to increase, and the calorie density of the portions eaten has also increased through food processing. Studies have shown that the number of calories eaten by the average American increased by 200 between 1993 and 2003, about 8%. Fast-food outlets encourage people to "super size" and buy "value" meals that include extra items such as fries and sugar load drinks. Most restaurants offer massive portion sizes and many courses. Americans seem determined to get as much food as they can for their money.
Food processing leads to major increases in calorie density - you get many more calories in the same serving of food. Conversely replacing a high density food such as bread, with a low density food such as celery gives you the same sense of fullness, but for only 5% of the calories.
Eating more food than necessary – particularly foods which are both high in sugar and fat can cause weight gain because your body coverts the excess into fat.
Foods that are not very filling, yet are high in calories, are also a problem because you get hungry and eat between meals.
According to Dr. Marion Nestle, at the Department of Nutrition and Food Studies, New York University, the average person consume 3,800 calories of food a day - 500 more calories than 30 years ago, and his may be partially because food is cheaper now. The increased consumption of calorie-dense foods and lower exercise patterns are also major problems.
Less than 30% of American adults complete at least 30 minutes of moderate pace walking or other moderate activity on most days of the week. Almost 50% do no exercise at all. Almost 50% of high school students in America watch more than two hours of television every day. This lack of physical activity is listed as a cause of obesity - people are eating more calories and burning less, so that the number excess calories going to fat has increased.
Burning as few as 100 calories a day by taking a brisk walk for about 20 minutes is equivalent to a weight loss of about 5 kg a year, while walking for 60 minutes burns an extra 300 calories per day leading to a potential weight loss of about 15 kg. Any aerobic exercise, such as swimming, jogging, skiing, bicycling or dancing can be beneficial. Despite these assertions there is very little god data on the contribution of low exercise rates to obesity. According to existing surveys, only 20 percent of the population are frequent exercisers.
The combination of a reduced-calorie diet and increased physical activity will lead to better weight loss than either one done separately. Small changes in diet and physical activity done each day is the key to long-term, successful weight loss for most obese people.
Conclusion - What is the Cause of the Obesity Epidemic?
The fundamental principles are simple:
The Solution -