Losing weight safely: advice from a bariatric surgeon

Does the recommended speed of weight loss depend on how big you are to start?

The heavier you are to begin with, the more quickly you’ll lose weight with a well-controlled diet and increased exercise. People with just a bit of excess weight will find that it takes them much longer to shift a few pounds than someone severely overweight who has started following recommended calorie and nutritional intakes.

Do the NHS guidelines of 0.5-1kg per week apply to everyone?

For most people, losing no more than a kilogram a week should allow healthy and maintainable weight loss. Though you may find that you lose a significant amount more in the first week or so of a new diet programme as “water weight” drops off. However, the key to effective weight loss is finding a sustainable programme and personalised lifestyle changes that you can keep up on a long-term basis, and so making more gradual changes are more likely to stick than anything too radical.

What are the dangers of losing weight too quickly (eg nutrient deficiencies, light-headedness) and the psychological downsides?

Along with being unsustainable, losing weight too fast can also have a negative effect on your health. So-called “crash-dieting” can leave you at risk of nutrient deficiencies, and the health conditions associated with them such as hair loss and lost bone density, if you cut out key food groups or aren’t eating enough. Equally, you may find that your muscles deplete if you’re dieting too excessively, or your metabolism drops, which can counter any weight loss efforts you’re making. Gallstones are a common side effect of rapid weight loss, in fact for our bariatric weight loss surgery patients we often prescribe a 6 month course of treatment to prevent gallstones following their operation, as they can be very uncomfortable for those affected.

Not eating enough can also affect your ability to function, mood and sleep quality. You’re better off making healthier choices, cutting back on high-calorie options like ultra-processed foods including ready meals and some cereals, sugar and alcohol than restricting how much you eat or limiting important nutrients.

Is there statistical evidence that the speed at which you lose weight has a bearing on how likely it is that you maintain that weight loss?

While there’s no statistical evidence, there are a number of indicators and qualitative research cases that show those who undergo rapid weight loss are more likely to regain. The real impact of any weight loss should be holistic – even for diets, weight loss attempts often fail when not made as part of a significant lifestyle change. You should be assessed by a psychologist, nutrition expert and, if appropriate, a surgeon with a specialism in obesity management to provide you with a programme you can maintain for years to come.

If you don’t care about regaining the weight (eg you just want to look “good” for your holiday and that’s that) then does it matter if your programme isn’t sustainable.

Even if you’re not concerned about the long-term sustainability of a diet, rapid weight loss isn’t advised unless it’s supported by qualified experts and done in a controlled manner. Aside from the mental health risks of conditions like anorexia and dysmorphia that can come with rapid change in physical appearance, highly restrictive dieting can have a long-term impact on your body, from menstrual cycle to loss of physical fitness. If you want to get in shape for a particular event, like a wedding or a summer holiday, it’s still best to lose the weight gradually beforehand to limit the negative effects on the body and use the event as an opportunity to start the process for longer term change.

• If you’re worried about your weight, speak to your GP about possible treatments. (Don’t have a GP?)
• King Edward VII’s Hospital’s Bariatric Surgery service brings together expert surgeons, dieticians and support staff. Find out more how we can help you.