Scientists say that when it comes to losing weight, there is no one-size-fits-all set of instructions. Instead, different diets suit different people, depending on their DNA.
This means that while the latest miracle diet might help your friend drop a dress size, it could do you a fat lot of good.
And official weight loss advice may not help as many people as hoped.
Researcher William Barrington told a conference in Florida: ‘There is an overgeneralisation of health benefits or risks tied to certain diets.
'Our study showed that the impact of the diet is likely dependent on the genetic composition of the individual eating the diet, meaning that different individuals have different optimal diets.'
To make the find, Dr Barrington, of Texas A&M University, fed mice one of five different diets for six months.
Some were given a typical Western diet, others a traditional Japanese diet, a Mediterranean diet, a high-fat low-carb Atkin’s-like diet or normal mouse food.
Importantly, he used four different strains of mice, to mimic the genetic differences in four unrelated people.
All were allowed to eat as much as they wanted and their meals were made as realistic as possible, with rice and green tea extract part of the Japanese diet and red wine extract included in the Mediterranean plan.
Tests showed the creatures’ health varied greatly, with some strains faring better on some foods than others.
For instance, while a fatty, sugary Western diet fuelled obesity, the severity depended on the strain.
And one lucky strain seemed immune to the effects of eating badly, The Allied Genetics Conference heard.
Plus, some mice were healthier on everyday Western food than on the plan similar to the fat-heavy, carbohydrate-light, Atkin’s diet that has long been popular with slimmers.
Other mice liked the fatty food in the Atkin’s-like diet so much that they gorged on it and became obese.
Dr Barrington said: ‘Given the metabolic and genetic similarity of humans and mice, it is highly likely that the level of diversity of diet response seen in our study will also be observed in humans.’
‘We’ve largely viewed diet the same way for the last 100 years - assuming that there is one optimal diet.
‘Now that we’ve identified that this is likely not the case, I think that in the future we will be able to identify the genetic factors involved in the varying responses to diet and use those to predict diet response in humans.’
In other words, it might eventually be possible to pinpoint the best diet for an individual person by giving them a genetic test.
In the meantime, the researcher says we shouldn’t use his results as an excuse not to diet. Instead, we should persevere and if the first diet we try doesn’t work, try another one.
Dr Barrington said: ‘If one tries a diet and the results are not as they had hoped, it could be that particular diet is changing metabolism in a way that is not conducive to fat loss.
‘So, one should be open to changing diets if the results are not as expected.
‘What we are finding is that a diet may be great for one individual, but terrible for another.’
Matthew Capehorn, of the Rotherham Institute for Obesity, echoed the advice, saying ‘the secret to successful weight loss is to find what works for you’.
However, he cautioned that human obesity is much more complex, with everything from emotions to cooking skills affecting a person’s diet.
Dr Capehorn said: ‘In humans we have to face psychological hunger.
‘If after an evening meal we get the munchies after an hour or two, in front of the TV, this is psychological hunger, as physiologically we should be full for 6 to 8hrs.
‘Equally in a restaurant, we may actually be full after the starter but, because we have paid for the meal, we still eat the main course.
‘After that, and even although we are stuffed, we often give in to the temptation of the dessert.’