27 February 2006

Leptin - the answer to obesity?

Can one use leptin to lose weight? What are the pros and cons? And what do the researchers say? DietDoc takes a closer look at this hot topic.

Leptin has become a buzzword in weight-loss circles. Many people want to know where they can obtain leptin treatment and there is much talk of doctors who inject their patients with leptin to promote weight loss.

In view of the interest in this new hormone, we need to consider what we know about its functions in the human body and whether it can really help people to lose weight.

Preliminary research
Leptin (Greek: leptos = thin) hormone was discovered about a decade ago.

It is a hormone that is produced by the so-called ob gene and is secreted by adipose tissue (fat tissue) when the amount of fat in the body increases. Leptin is regarded as a sort of 'watchdog' that monitors how much fat the body contains.

Secretion of leptin in experimental animals in reaction to weight gain, reduces hunger (thus reducing food intake) and increases energy expenditure (the two goals of most weight loss regimens), which leads to weight loss so that the fat balance of the body is maintained within normal limits (Cena et al 2002).

Quick fix? No
When the general public was introduced to leptin and heard that it can suppress appetite and increase energy expenditure to produce weight loss, they were ecstatic.

Here was the answer to every dieter's dreams: take leptin and it would reduce food intake, increase energy expenditure and boost weight loss.

Alas, ten years down the line, researchers investigating the role of leptin in humans, have come up with plenty of new information about this hormone, BUT (and it is big but) there is no evidence that a simplistic approach to the use of leptin in human beings will help with weight loss.

Why not?
The reason why leptin supplementation does not work in most human obesity cases, is that only those individuals who suffer from a genetic leptin deficiency (i.e. their genes do not produce any leptin), will react to leptin treatment by losing significant amounts of weight.

So, if you are one of a very small percentage of people (approximately 5%) who was born with a leptin deficiency (which would have manifested itself by causing massive obesity from a very early age), leptin treatment is the answer (Sinha & Caro, 1998).

If you are, however, one of the millions and millions of overweight and obese individuals who were not born with a genetic leptin deficiency, then taking leptin as a medication will not make much difference to your body weight.

The reason for this frustrating situation is that researchers have found that the majority of obese people produce masses of their own leptin, BUT that this leptin just does not do its job properly.

The high levels of circulating leptin found in obese and overweight patients do not reduce food intake by suppressing hunger and they do not increase energy expenditure to promote weight loss.

In other words, obese patients don't need more pharmacological leptin. They are already making more than enough of their own, but the leptin they produce is not effective. Scientists have compared this situation to insulin resistance, and suggest that obese individuals are 'resistant' to the leptin they produce.

So, the 'magic bullet' of leptin appears to be another quick fix that has not materialised. It's no use treating obese patients with leptin, because they make more than enough leptin in any case, but their bodies can't use it properly.

A glimmer of hope
Researchers are, however, not daunted by the discovery of 'leptin resistance' and the failure of leptin treatment to date. Many studies continue to be conducted to discover more about this once-promising weight-regulating hormone.

A study reported recently in the Arbor Clinical Nutrition Updates (2005) found that leptin may help to prevent patients from regaining weight after weight loss induced by energy restriction and/or exercise.

Ten volunteers, who had lost 10% of their body weight using a very-low-energy liquid diet, were given leptin injections. Their body reactions to this weight loss were monitored.

Weight loss is usually accompanied by a decrease in total energy expenditure, improved muscle efficiency, reduced use of glucose as an energy source and reduced levels of thyroid and epinephrine (all of which can sabotage further weight loss and usually result in a regain of the lost weight).

The leptin injections used in this study significantly reduced all these weight-loss hampering effects that are induced by the body to counter weight loss.

Although further research is required, leptin may be useful as a treatment to prevent slimmers from regaining all the weight they lose.

Another study found that leptin may be beneficial in the treatment of lipodystrophy syndrome (a condition linked to insulin resistance that is occurring more frequently nowadays as part of the metabolic syndrome and in HIV patients treated with antiretroviral therapy).

Less positive findings are that obese women have much higher circulating levels of leptin and are more prone to 'leptin resistance' than men. This may be one of the reasons why women are more susceptible to overweight and experience more problems with losing weight than men (Kennedy et al, 1997;).

Where do we stand?
We now know that leptin is not a 'magic bullet' or a 'quick fix'. Unless you suffer from genetic leptin deficiency, using leptin will not help you to lose weight.

If you are overweight or obese, you are already producing a lot of leptin, but it won't do its job, so taking more leptin won't help.

Future research may come up with weight loss solutions that make use of leptin, for example drugs that can counteract 'leptin resistance' in the same way that drugs like glucophage are used to counteract 'insulin resistance', or leptin may be used to prevent regain of weight after a weight loss regimen.

Can I buy leptin in South Africa?
No. Leptin is not yet commercially available in South Africa. And please keep in mind that, even if you are totally desperate to 'try anything' to lose weight, you are making more than enough leptin already if you are obese and don't need more.

In fact, taking more leptin if you are obese may complicate matters and worsen 'leptin resistance'.

Until researchers have unravelled the mysteries of leptin and come up with safe solutions, stick to an energy-reduced, balanced diet and exercise to shed those unwanted kilos. – (Dr Ingrid van Heerden, DietDoc)

(References: Arbor (2005). Leptin & obesity. Arbor Clinical Nutrition Updates, Vol 240:1-3; Cena H et al (2002). Obesity etiology: role of leptin. Minerva Gastroenterol Dietol, 48(4):303-8; Kennedy A et al (1997). The metabolic significance of leptin in humans: gender-based differences in relationship to adiposity, insulin sensitivity and energy expenditure. J Clin Endocrinol Metab:82(4):1293-300. 303-8; Sinha MK, Caro JF (1998). Clinical aspects of leptin. Vitam Horm,54:1-30 )


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