Academics said that the number of obese people was continuing to grow, but the gyms seem to do pretty little to stem the tide.
Dr Jennifer Smith Maguire, of the University of Leicester, said private gyms were mostly used by richer members of society - leaving the less well-off struggling for help to combat weight problems.
And they also promote exercise not as a part of everyday life but as something to be "squeezed" into the daily routine and focus on looking healthy for image and not health reasons.
Dr Smith Maguire's research focused on the USA, where there were around 20,000 commercial health clubs in 2002. By comparison, the UK that had a much stronger tradition of the collective provision of recreation such as leisure centres boasted of fewer than 2,000 private gyms. China had only 350.
She said, "Over recent decades, many Western countries have experienced a strange paradox, with fitness and exercise industries expanding alongside problems of inactivity and obesity.
"The commercial fitness industry benefits from the scientific legitimacy and political urgency bestowed on population health issues such as inactivity and obesity. But it is ill-equipped to address those issues for a number of reasons.
"In the US, for example, half of commercial health club members are in the top 20% of income earners.
"At the top end of the market, high income earners can afford excellent services and an 'enlightened' approach to fitness but at the bottom end of the market, middle and lower income earners can afford fewer and lower quality services and a 'factory' approach to fitness.
"And at the very bottom, excluded altogether from the market, are those individuals most likely to be inactive and obese.
"Physical exercise can be reintroduced as an integral part of everyday life, rather than yet another activity to be squeezed into an already shrinking supply of free time."
The extent of Britain's obesity epidemic was laid bare last month in a government report which warned 60% of men and 50% of women are predicted to be obese by 2050 and will cost the country £45bn a year. By then, only 10% of men and 15% of women will be the right weight for their height.
Welsh figures reveal 60% of men and 50% of women are already either overweight or obese.
Mary Sheppard, director of Fitness Wales, the governing body for exercise and fitness, said that gyms did have a part to play in helping the public build activity into their daily life. But she said that gyms were not necessarily suitable for all.
"Gym chains can sometimes be cheaper than local authority leisure centres and it can be easier, especially in winter, to go to a gym rather than for, say, a bike ride."
And Fred Turok, chairman of the Fitness Industry Association (FIA), "The industry has the expertise, the resources and the capability to help address the current public health crisis, but it can only work with those who choose to do something about their condition."