Fad weight loss plans only result in loss of body fluid not fat, experts warn

Miracle diets can never work and it is impossible to lose more than two pounds a month, a new study claims.

Groups of cyclists were tracked to see how their fat levels changed during and after exercise.

But even after consuming a popular fat burner - p-synephrine - the maximum amount of fat they could burn was 0.001lbs (0.7g) a minute, or 0.09lbs (42g) an hour.

It means that even with a supplement, an individual could not burn much more than 2.2lbs (one kilogram) a month.

Fad diets that lead to a more dramatic weight loss are mainly related to a loss of fluid in the body - which will creep back over time - according to the study.

'It's less attention-catching than miracle diet slogans, but scientifically speaking, effective change would be at that rate,' lead author Juan Del Coso, a researcher from Camilo José Cela University in Madrid, said. 

'The rate of loss could increase with p-synephrine, but always combining the substance with exercise.'

Still, he says, it is not possible to burn much more than two pounds of fat.  

'That should be the aim: to lose a kilo per month, but a kilo of fat,' he said. 

The research published in the British Journal of Clinical Pharmacology focused on one particular fat-burner: p-synephrine.

P-synephrine is an alkaloid that can be found in nature (although at low concentrations) in a wide variety of citrus fruits such as oranges, mandarins and grapefruits.

Commercially it can be found in greater concentrations as extract of bitter orange. 

Because of its chemical similarity to ephedrine (a nervous system stimulant), and the substance's activation of key receptors, it has become a popular food supplement, typically included in weight loss products.

The advantage of p-synephrine is that it has very little impact on heart rate and arterial tension. 

It means it has fewer side effect than other adrenaline stimulators.   

The purpose of the investigation was to determine the rate of fat and carbohydrate oxidation - during rest and exercise - after taking a high concentration of supplement. 

In a randomized, placebo-controlled, double-blind, experimental study, 18 subjects underwent two experimental trials.

The first involved exercising after consuming p-synephrine (3 mg p-synephrine per kilogram of body mass).

The second was after taking a placebo (control test).

An hour after ingesting the substance, energy expenditure and arterial tension were measured.

It was measured again after physical activity, in this case using a static bike. 

Acute p-synephrine ingestion had no effect on energy expenditure, heart rate or arterial pressure.

The substance did produce a notable change in substrate utilization during exercise: ingesting p-synephrine before exercise increased the rate of fat oxidation.

It also reduced carbohydrate oxidation at low and moderate intensity.

In fact, p-synephrine increased individuals' maximum capacity to burn fat, although it did not change the intensity at which this was attained. 

This data suggests that p-synephrine supplements could be useful to increase fat oxidation by 0.02lbs (7g) per hour of exercise.

But even with that boost, it meant they were not burning more than 0.09lbs (42g) an hour. 

The authors highlight the need for further study to determine the effects of the long-term use of this substance on energy production, metabolism at rest and substrate utilization during exercise. 

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