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Is the 3500-calories rule even true?
If you follow conventional weight-loss wisdom, then you are setting yourself up for disappointment.
The "3500 calories per pound of fat" rule is applied to mean that if you maintain a deficient of 500 calories each day that you will lose one pound of fat each week. This doesn't work for long-term weight loss. Modifying your expectations will keep you motivated to keep going. The reality isn't as exciting, but it sets you up for success.
I became interested in the origin of the rule. When I searched, it turned out to be a little vexed.
The source of the idea that burning one pound of body fat required 3500 calories - more specifically a deficit of 3500 - seems to be lost in time*. Denise Webb, PhD and Registered Dietician said in an article titled "Farewell to the 3,500-Calorie Rule": Ask any dietitian and he or she likely will say that cutting food intake by 3,500 calories results in a 1-lb loss. Cut 500 calories per day and that's 1 lb per week. Over the course of one year, that would equal 52 lbs. That's what RDs have been and continue to be taught, and it's promulgated by the US Surgeon General and the Academy of Nutrition and Dietetics, and it's repeated in several nutrition textbooks. It's been estimated that the 3,500-calorie rule is cited in more than 35,000 educational weight-loss sites.
Huffington Post's K. Aleisha Fetters said:
Years ago, scientists played around with a pound of squishy, slimy human fat and found that it contained 3,500 calories of energy.
And Dr Zoe Harcombe PhD was more scathing:
One of the most commonly held diet myths is "To lose one pound of fat you need to create a deficit of 3,500 calories"... You will see this formula in government literature, in just about every diet book, in private health booklets and all over the internet. The next time you see it, or hear it, ask where it comes from. You will not get an answer. (I asked the following seven UK organisations: the National Health Service (NHS); the National Institute for Clinical Excellence (NICE); the Department of Health; the National Obesity Forum; the Association for the Study of Obesity; the British Dietetic Association and Dieticians in Obesity Management and five of these have no idea where it even comes from. How many calories are there then, in body fat?
Is the 3500 calories rule true or not true, and how reliable is it?
The comments above raise two questions:
(From here I am going to work in metric quantities, as more information is published in metric.) How many calories are there in 1kg of body fat? Dietary fat and body fat are not the same. "Body fat" is a complex organ known as adipose tissue. It's this that you "burn" when losing weight. Fat is one component of the weight of adipose tissue. Estimates differ as to the proportion of fat in adipose tissue. A recent reliable scientific estimate is that an average fat content of 80% and water content of 15% can be used. Here's the calculation using an average fat content of 80% for body fat:
I'm going to declare these two numbers (7,200 & 7,700) to be equivalent. We're dealing with estimates here. The average fat content of adipose tissue and the average number of calories represented by 1kg fat are each approximate. As the Mythbusters would say - Myth Confirmed! It's easier to change expectations than human nature
Now the question is, why doesn't a deficit of 500 calories a day work for the long term?
For the short-term a 500 calorie a day deficient can work, provided that you can get through various plateaus. One plateau usually occurs relatively early, due to cessation of the early loss of water associated with glucose storage. Another often happens at about 6 months, due to inconsistencies in habits creeping in - snacks, cravings, pulling back from exercise. A third plateau starts at around 12 months, when your body becomes fully adapted to the deficit regime and is reluctant to give up more fat. Your body has gone into survival mode and is hunkering down for the long term. These plateaus are one reason that hanging on to the goal of dropping weight by 1kg per fortnight, as a result of a deficit of 500 calories a week, leads to failure. Over the longer-term, your body is not going to give up 1kg per fortnight - despite the calorie deficit. Problems arise when this measure is your key source of motivation. The main reasons found by researchers for the slowing in weight loss are that such dieting leads to dynamic changes in energy balance and physiological adaptations. These act to counter the earlier rate of fat loss. The other major reason is that people don't stick to the prescribed reduced-calorie diet long term - it's too hard. These three factors above - energy balance, physiological adaptations, and dietary variations - are "reality". Biology determines two or them and one is human nature. Expect 1/3 of the weight loss of the 3500 calorie rule
The answer lies in modifying our expectations.
Mathematical biologists have formulated sound estimations of expected outcomes of a 500 cal/day reduction in food intake - over the long-term. Their models predict that over three years, the results will be about one-third of the expectations of the "3500 calories rule". Using their predictions I found that the "3500 calorie rule" estimated a weight loss 3.13 times greater than their models estimate. That's because their models account for both biological and human behaviour and motivation. You can hit your goals if you are consistent
If you want to lose a large amount of weight, then set yourself a long-term target.
The 500-calories a day deficit will get you there, but not at the ratio of 1 kg each two weeks. Your best expectation is to plan to achieve one-third of the estimate given by the "3500 calories rule", and keep going. Over three years you could expect to maintain a loss of about 8kg per year. More initially, less later. It sounds slow, but it's better than starting every year with high expectations and not being able to complete a single 12 month period, and having to start again. Slow and steady beats the dieting yo-yo. If you can stick with a steady deficit over the years, then you will hit your weight-loss goals, and be very likely to be able to maintain them. Add consistent exercise and you will lose more fat and less skeletal muscle. Most people fail because their expectations are too high - if you are more realistic from the start, then you are much more likely to succeed. Good luck.
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* Denise Webb (quoted above) actually provided the exact source for the "3500 calorie rule":
It originated from researcher Max Wishnofsky, MD, in 1958, who calculated that 1 lb of fat stores approximately 3,500 kcal of energy.  RSS Feed
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