Weight has become an obsession. One of the first questions asked after a baby is born is “how much did he/she weigh?”, and “you look like you’ve lost weight” is almost invariably meant as a compliment. It is not just the Jewish community who have this fixation. According to research carried out in 2016 by Mintel, two thirds of UK adults are on a weight-loss diet “most of the time”. In my busy north London nutrition practice, 70 per cent of clients seek my help for weight loss.

Nearly 62 per cent of England’s population are overweight or obese, making the UK the “fat man” of Europe according to the Academy of Medical Royal Colleges. But does it matter? We love to celebrate with food and it is a huge part of our culture. Is it OK to have a bit of a wobbly tummy, or should we all be trying to slim down?

Weight is determined using the body mass index (BMI), calculated simply by dividing a person’s weight in kg by the square of their height in metres. The resulting number corresponds to a category — underweight (less than 18), normal weight (19 to 24), overweight (25 to 29) and obese (30 plus).

The BMI has been used by medical professionals for more than 100 years but regularly comes into criticism for being too crude. For example, muscle mass is not considered. This means a very fit, muscley athlete might have a BMI in the obese category, while a short person might have a healthy BMI despite carrying too much weight around their middle (the dangerous area). A more revealing determinant of health risk is waist-to-height ratio. For this, divide the waist circumference by the height (ensure both units are the same). A result of 0.4 to 0.5 is considered “safe”. Lower is underweight and a result of 0.5 or more signifies increased risk of heart disease, stroke and death.

Although BMI may be flawed when looking at individuals, it can be useful when studying populations and it is this measure that is used in most of the studies into weight and disease risk.

Whether you can be healthy and under- or overweight is the subject of ongoing research. We do know the risk factors for certain diseases are increased when you are overweight — these include cancer, diabetes, heart disease and stroke. However numerous studies have looked at just one disease to see if weight makes a difference and the findings are not always conclusive, or as you might imagine.

For example, a 2016 Israeli study of nearly 100,000 Jewish women compared their BMI when adolescent (1967-2011) and breast cancer incidence by the time they were menopausal. Participants who developed breast cancer pre-menopause were more likely to have been underweight as adolescents, whereas those who were obese or overweight had no more significant risk; in fact, the researchers conclude, their weight might have been protective (Keinen-Boker et al, Breast Cancer Research and Treatment, July 2016).

Another study found underweight people with heart disease were four times more likely to die from it than those who were overweight. (Curtis et al, JAMA Internal Medicine, 2005).

Fat as a protective measure probably stems from human evolution, as I tell my clients if they are struggling to lose weight. When we were hunter-gatherers, it was a time of feast and famine (think of lions on a hunt in any David Attenborough documentary). Only people who were good at storing weight would have survived.

Our modern lives are much more focused on feast than famine and there is reason for concern. New research for the University of Birmingham, presented (but not yet published) in May this year, looked at the risks of being overweight or obese and found, despite previous findings, there is an increase risk from excess weight and chronic disease. This study is the largest of its kind, looking at the health records of 3.5 million people between 1995-2015. Researchers found obese individuals who “appeared healthy” — no diabetes, high blood pressure or abnormal blood fats — had a 50 per cent higher chance risk of coronary heart disease than those of a normal weight. They also had a seven per cent increase in risk factors for stroke and double the likelihood of heart failure.

Putting aside the prospect of chronic disease for a moment, from my own clinical experience, I find my overweight and obese clients often feel their weight is negatively contributing to health symptoms. Joint pain, breathing issues, digestive problems and self-esteem are all affected by excess weight and, when my clients start to lose weight — but more crucially start eating a nutritious diet — their symptoms reduce.

Conversely, I have treated clients who were recovering from eating disorders and, though their BMI was in the healthy range, were still suffering the consequences of being underweight — nutrient deficiency, fatigue and lack of menstruation.

So it is hard to establish if being outside the healthy BMI is always detrimental to health. But all researchers agree on the importance of being physically active, eating a nutritious diet of whole food, vegetables and good fats and sleeping well. Recent headlines even claimed: “Sitting all day is worse for your health than smoking” and “A good night’s sleep can ward off heart disease and diabetes”.

Weight can be an issue for your health but, if you are concerned, instead of starting an extreme weight-loss diet, take stock of your lifestyle. If you do little physical activity, are very stressed, eat a high-sugar, high-processed-food diet or sleep poorly, these things are more likely to affect your health than whether the trousers you wear are a size 14 or an eight.

Laura Southern is a nutritional therapist practising in Finchley, north London, londonfoodtherapy.com