Last updated on Jan 18th, 2021 at 01:14 pm

Do you think sex is a great workout? Do you think itâ??s better to lose weight slowly and steadily instead of all at once? These are some commonly-held beliefs about weight loss that are actually not based on any real evidence. 

In an article published this week in the New England Journal of Medicine, a group of researchers set about exploding seven common myths about obesity and weight loss. According to the authors, their intention is to set the scientific record straight and to help people understand how better to judge claims about weight loss, and thus to be more effective dieters.
Myth #1: Small sustained changes in energy intake or expenditure will produce large, long-term weight changes
You often hear advice like â??try cutting just 500kj a day and you could lose 5kgs a year without changing anything elseâ?. This advice is based on the idea that there are a certain number of kilojoules in a kilo of body fat, and if you reduce your kilojoule intake by that amount over a given period of time, youâ??ll lose that kilo.
This is sound reasoning up to a point, say the researchers, but it doesnâ??t work in the long-term. Instead, what happens is that as you lose weight, you need to keep adjusting the amount you eat to keep pace with your reduced energy needs â?? bigger people burn more energy than smaller ones. After youâ??ve lost that first kilo, you need to cut slightly more energy from your diet to lose the second, and so on.
Bottom line: weight-loss is a dynamic process, and you need to keep adjusting your diet to keep losing weight.
Myth #2: Setting realistic goals for weight loss is important, because otherwise patients will become frustrated and lose less weight.
Weight-loss gurus often tell dieters to set realistic goals â?? plan to lose 5kgs in 6 months, not 50 â?? to avoid becoming discouraged and frustrated and giving up on their diets. There is, however, no scientific reason to think that this is necessary. In fact some research suggests that setting ambitious goals can actually motivate people to stick to tough diets.
Bottom line: set whatever goal you find inspiring.
Myth #3: Large, rapid weight loss is associated with poorer long-term weight-loss outcomes, as compared with slow, gradual weight loss
You often hear that itâ??s best to lose weight slowly, half a kilogram a week, because rapid weight loss isnâ??t sustainable. However, the evidence suggests that this isnâ??t true. Some studies have found no long-term difference in body weight between those who lost weight rapidly and those who lost it slowly, while other studies have indicated that substantial, rapid early weight-loss was actually associated with a lower long-term body weight.  
Bottom line: if you find it motivating to lose weight fast, especially at the start of a diet, go for it.
Myth #4: It is important to assess the stage of change or diet readiness in order to help patients who request weight-loss treatment
Sometimes doctors argue that patients need to be â??readyâ? to lose weight before beginning a diet, and that itâ??s therefore necessary to measure which stage of change patients are at. Although this advice seems like good common sense, thereâ??s no scientific evidence to suggest that itâ??s true. In fact, patientsâ?? initial state of readiness is not associated with how much weight they lose when dieting.
Bottom line: doctors should recommend weight loss plans to obese patients who need them without worrying about whether or not the patient is truly â??readyâ?.
Myth #5: Physical-education classes play an important role in reducing or preventing childhood obesity
Although lots of people think that PE classes at school are an important tool for preventing childhood obesity, all the studies on the effect of PE on kidsâ?? weight have shown no significant effects. Apparently two sessions of PE a week is just not enough to keep kids thin.
Bottom line: if you worry about your childâ??s weight, you need to make sure he eats right and exercises regularly above and beyond PE.
Myth #6: Breast-feeding is protective against obesity
This is one Iâ??ve heard often from young mothers â?? the belief that breastfeeding your baby will help prevent her from becoming obese later in life. Itâ??s a nice idea, but is sadly not backed up by any scientific evidence.
Bottom line: breastfeeding has many benefits, but fending off fatness in your baby is not one of them.
Myth #7: Having sex burns 400 to 1200kj for each participant.
Ah, if only this were true â?? that an energetic love fest was as good as run in the park. Unfortunately, while sex is certainly more fun than running, it sadly does not burn many kilojoules. According to the researchers, â??a man weighing 70 kg would expend approximately 15kj per minute during a stimulation and orgasm session. Given that the average bout of sexual activity lasts about six minutes, a man in his early-to-mid-30s might expend approximately 90kj during sexual intercourse. Of course, he would have spent roughly one third of that amount of energy just watching television, so the incremental benefit of one bout of sexual activity with respect to energy expended is plausibly on the order of 60kj.â?
Bottom line: romping is (tragically) no substitute for running

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