The statement ‘eat 3,500 fewer calories a week’ (or use up 3,500 calories by exercising) to lose 1lb is not only ubiquitous, it is stated as fact. The problem is, it’s wrong.
Who peddles such nonsense?
• The NHS
• The Department of Health
• Weight Watchers and similar national diet groups
• The British Dietetic Association
• The Association for the Study of Obesity
• Many (in fact all I can find) accredited nutrition courses
• Most GPs
• Most dieticians and other dietary therapists
• The media (TV, newspapers, magazines, etc)
• Text book writers (school biology books, for example); to be fair, most of them are following the publishers’ wishes. But, still…
Even at small group levels, people’s weight loss/gain varies.
Zoë Hellman, Weight Watchers dietician, says, ‘One pound of fat contains 3,500 calories. To lose 1lb a week you would need to cut out 3,500 calories from your overall weekly nutritional requirements, this equates to needing a deficit of 500 calories a day.’
Essentially, in terms of diet and weight loss/gain, a calorie is not a calorie: a calorie is a measure of the chemical energy within a food (or piece of coal, for example) that is released as heat (light too, if it’s not in our bodies) when burned in a bomb calorimeter – and that is in a closed system, not a human body.
There are approximately:
• 4 calories in a gram of starch or sugar
• 4 calories in a gram of protein
• 7 calories in a gram of alcohol
• 9 calories in a gram of fat
However, calories from different sources are not created or used equally! There are calories in coal and wood, for example. Factors affecting how quickly the calories from our food and drink are stored or used include (very simply):
• Your basal metabolic rate (BMR): this is what keeps you ticking over, and uses a large proportion of the fat, protein, vitamins and minerals you eat
• What you eat:
o excess carbohydrates will be stored first as glycogen and, when those stores are full, as fat
o excess amino acids (broken down proteins) are deaminated (broken down into amines and glucose); the glucose, if not needed, will be stored as fat
o excess fat, if eaten without carbohydrates, will circulate until used up by your cells
o excess fat, eaten along with carbohydrates, will be stored as fat
o Your body uses up about four times more energy to digest (break apart) 100g of protein than it does to digest the same amount of starch
o Gut bacteria have an effect on what is absorbed or not: people who are obese have different gut bacteria to those who are slim, for example
• If one is insulin and/or leptin resistant, then appetite control can be problematic, as can accessing fat stores to burn up the fat
• Fructose is a sugar, but it’s metabolised differently to glucose and has different effects on the body and satiety
• Burning off calories as exercise and/or not eating enough both make you hungry and you will eventually seek out more food and/or move less
Put it this way, if total calories were really all that mattered and you and your friend both eat 2,500 calories a day, I could put you on a diet of 2,000 calories a day of usable carbohydrates (starches and sugars) and your friend on a diet of 2,000 calories of fat a day… and you should both lose weight, lose the same amount of weight at the same rate. It won’t happen. My book explains why.
So where did this concept initially come from? The answer is, no one knows. It appeared in non-body science, seemed to make sense in terms of ours bodies, and was adopted, apparently without question.