Before the popularity of celebrity magazines, newsagents shelves were dominated by slimming magazines and diets that calculated different ways to cut 3,500 calories - the energy content of one pound of body fat.
Before the popularity of celebrity magazines, newsagents shelves were dominated by slimming magazines and diets that calculated different ways to cut 3,500 calories - the energy content of one pound of body fat.
And it wasn't just the magazines that used this formula: for many years it was widely accepted within the medical profession and patients were told that if they could cut 500 calories per day from their diets (adding up to 3,500 per week) they could lose a pound of fat each week.
However, as many would-be dieters have discovered, it might work for the first week, and maybe even the second and third, if you have a lot of excess weight to lose, but eventually this formula stops working and weight just frustratingly tapers off and plateaus.
Losing muscle mass
The 3,500 calories rule is based on a calculation made by researcher Max Wishnofsky in 1958, who concluded that 1lb(454g) of fat stores approximately 3,500kcal of energy.
However, when a person starts to lose weight they won't just lose fat; they will also lose lean body mass, mostly muscle. Muscle mass can be preserved with the right type of exercise and by maintaining an adequate protein intake, but this will differ from person to person, making the 3,500 Calorie Rule inaccurate.
As you lose weight, your BMR (basal metabolic rate) drops and the calorie deficit is harder to maintain (unless you restrict your calories more and exercise more). For example, if your body needed 2,600 calories a day to be in energy balance and you reduced your intake by 500 calories to 2,100, you would lose weight.
But once you'd lose 20% of your weight, your body would only need 2,200 calories a day to stay in energy balance, so if you continued to eat 2,100 calories your weight loss would stall.
Calculating the deficit.
In addition to this, the longer you diet the more efficient you body becomes, as it makes metabolic adjustments in order to cope with the fact that it is receiving less food. Taking into account these factors, new, more sophisticated weight loss models have been developed. They calculate the number of calories needed to maintain energy balance based on an individuals baseline data - that is, their age, gender, size and body composition - and predict the calorie deficit required to continue to lose weight over time as some of the parameters change.
These models show that the 3,500 calorie rule is only valid (at best) for the first month after starting a diet. However, it should be remembered that the early rapid weight loss phase will mainly be thanks to loss of glycogen and water mass not fat.
This is not a bad thing; it's just how weight loss starts because when we reduce our calorie consumption, particularly of carbohydrates, our body feeds off the store of glycogen in our muscle tissue and liver. Glycogen is a mixture of carbohydrate and mostly water, so the first week of dieting always has the most dramatic result on the scales.
Overall, the body tries to prevent excessive swings of either positive or negative energy but for those who want to lose weight this is often interrupted as diets not working. With a restriction of calories come a decline in metabolic rate, but if the energy deficit is high enough, the decline in metabolic rate will not be enough to negate it, and consequently both muscle and fat will be lost.
However, the loss of muscle will further decrease the metabolic rate and cause weight loss to slow to such an extent that the results become unnoticeable, at which point many dieters lose motivation and give up.
Diets do work but they work much better in conjunction with exercise, especially resistance exercise that will maintain muscle mass.
The bottom line:
So what should you do if the 3,500 calorie rule stops working? You can aim to maintain a 20% calorie deficit through a combination of increased exercise and cutting calorie intake, but this relies on having a fairly accurate measure of your daily calorie expenditure.
The best thing to do, if you were serious about losing body fat would speak to a physician and/or contact a reputable nutrition coach.
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