Dietary emphasis among kidney patients has, in the past, been on preventing and treating malnutrition, a condition which affects between 30 and 70% of dialysis patients. It is also prevalent in the pre-dialysis stage.

As the treatment, and hence the life span, of kidney patients have improved it has become apparent that the other main causes of illness and death among kidney patients are cardiovascular disease (CVD) and cerebrovascular disease. The risk of these complications is further increased in those who also have diabetes and hypertension.

In addition, medication prescribed for some of the auto-immune diseases and the anti-rejection drugs used in transplantation can increase risk factors for CVD because they encourage unwanted weight gain, steroid-induced diabetes and hyperlipidaemia.

CAPD can also lead to weight gain through absorption of glucose from the dialysate bags.

Finally, exercise and strength tests have shown how unfit and weak many renal patients are in comparison with healthy people of the same age and sex. This will undoubtedly increase the risk of their becoming obese as their energy expenditure is low.

Dialysis patients

Some studies have claimed to have shown that greater body mass index (BMI) is associated with a decrease in relative risk of death in dialysis patients. But a closer inspection of these studies reveals that it was not that overweight dialysis patients were living longer; it was that underweight patients had a greater risk of death. But then, we know this already.

However, in older people it is perhaps beneficial to be a little overweight and a large proportion of the dialysis population is now over 60 years of age.

Transplant patients

Weight gains of 10kg are common in the first year after transplant.

As many patients are underweight to start with, it could be argued that weight gain in these patients is acceptable. But the numbers of overweight and obese patients also increase, which is not ideal as these patients usually have additional risk factors for CVD.

Studies have supported the fact that pre-operative obesity is correlated to post-transplant weight gain - therefore attention should be paid to these patients in the pre-transplant period. A study involving 131 centres and 26,500 transplant patients showed an increased rate of kidney loss with increasing BMI. With a BMI > 33, there was a 38% and 28% increase in rate of kidney loss in men and women, respectively.

Early, intensive, dietary and lifestyle advice and follow up is effective in controlling weight gains in the first year post transplant.

Another study which involved small groups of patients attending a 10-week health, diet and exercise course for three hours a week based on the Health Education Authority's Look after yourself course, did not result in weight loss, but there were improvements in exercise ability, quality of life and dietary improvements involving decreased fat intake and increased fruit and vegetable intake. These factors can all reduce the risk of CVD despite the lack of weight loss.

How to treat obesity in kidney patients?

A combination of dietary advice, behavioural modification and a physical activity programme has been recommended in the SIGN guidelines and the Royal College of Physicians.

Programmes tend to be between 10 and 20 weeks and losses of 0.5kg a week have been achieved. Drop-out rate is 20% compared with a 58% drop out in general-hospital obesity clinics.

The emphasis is on achieving at least a 10% weight loss rather than trying to reach an "ideal" BMI.

A 10% weight loss has been shown to have health benefits: improvements have been seen in blood glucose, lipids, physical performance and well-being.

Dietary advice

The Health of the Nation paper in 1992 stated that the aim was to reduce saturated fat intake from 17% to 11% of energy intake and to reduce percentage of fat as energy in diet from 40% to 35%. And an overall Calorie reduction of between 500 and 1000 Calories a day has been shown to lead to weight loss.

Behaviour modification

This uses counselling techniques and cognitive behaviour therapy. One approach is to ask the patient to keep a record that includes:

		the time;
		place and amount of food eaten;
		type of food;
		emotional state at the time; and
		hunger at the time.

This can identify the triggers which lead to eating and changing this environment or learning how to respond differently to various factors or stresses may decrease the stimulation to eat.

Exercise

Consistency should be emphasised before concentrating on duration or intensity. Ten minutes of exercises four times a week is better than 30 minutes once a week because it is important for patients to develop a regular exercise habit. Intermittent activity at varying intensity is acceptable if 10 minutes of continuous exercise at a higher level of intensity cannot be done. People who have been sedentary have to gain confidence in their ability to move and exercise, let alone to be seen in public in exercise clothing, which often accentuates body size and shape.

The limiting factor in these programmes seems to be in the follow up period. Without regular reinforcement offered by group contact or continuing appointments with the therapist, 40% of weight is regained within one year later; and in five years the great majority have returned to pre-treatment weight.

Fat but Fit?

There is evidence that it is better to be overweight and fit (lower risk of death from all causes and CVD) than to be lean and unfit. People who were obese and unfit had a greatly increased risk of dying from CVD.

Drug therapy for weight loss

Sibutramine inhibits serotonin and noradrenaline uptake which leads to a decrease in appetite.

A randomised, controlled trial of sibutramine showed a weight loss of 4.4kg after one year. Longer follow up showed 43% had continued maintenance of weight loss at two years compared with 16% taking a placebo (patients were also given diet and exercise advice).

NICE recommends regular checks and treatment should only continue after three months if a 5% weight loss has been achieved.

Orlistat (Xenical) is a pancreatic-lipase inhibitor. It prevents absorption of approximately 25% of fat intake. It can bring about a 10% decrease in weight in the first year, with some regain in the second year. It is not advisable to use it for more than two years. Side-effects are caused by undigested fat in stools, which is offensive and leeches certain vitamins and minerals.

So, it is better to try diet, exercise and behavioural counselling first

Surgery

A gastric bypass is more effective than gastroplasty but vitamin and mineral deficiencies are common. Patients receiving a gastroplasty who previously had a BMI > 40 showed a weight loss of 30 to 40kg and a decrease in diabetes and other risk factors.

The American Obesity Association recommended in 1996 the following treatment decisions based on risk assessment judged by BMI and adjusted for co-mordid conditions.

		Drug treatment for patients with BMI > 30 or BMI > 27 with co-morbidities
		Surgical options for patients with BMI > 40 or BMI > 35 with co-morbidities

Tips to combat obesity.

		Obesity poses a significant health risk but this depends on sex, age and ethnicity.
		As the causes are multifactorial there is no simple method of treatment.
		Treatment must be intensive, prolonged and involve a combination of therapies
		Small modifications in diet and physical activity are more sustainable and will decrease the risk cardiovascular disease
		As prevention may be simpler than cure, aim for timely intervention.