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Q1: I am 59, live in France and have a sedentary occupation, pretty much desk-bound in my home office, have an underactive thyroid for which I am taking Levothyrox at 50mg per day. I have had a weight problem since the age of ten and so I grew up being very aware of the right things to eat and I am very strict with myself. I actually don't like sweet foods and I stick to a healthy, balanced diet that includes fresh fruit and vegetables, low-fat meats and slow-burning carbohydrates, usually totalling an average of 1200 to 1500 calories per day.

We never eat processed foods or take-away foods, and rarely eat in restaurants unless it's unavoidable, for example on business trips. Nevertheless, I am still very overweight and, according to online BMI calculators, need to lose 60lbs just to be on the borderline of "normal" and "overweight".

It is frustrating when seeking advice on weight loss to find that it invariably consists of ways to stop people from over-indulging. I have consulted doctors and nutritionists and they clearly don't believe that I don't overeat, so they have been no help at all.

I am now cutting that down to between 800 and 1000 calories per day and increasing my exercise routine, making sure that I do at least 30 minutes of brisk walking every day, plus some resistance exercises and tai chi. However, I have tried this so many times without success that I can't help feeling rather negative about my prospects.

I did notice over the years that my main periods of weight gain in adult life were during the time when I was taking birth-control pills (for four years) and again during menopause. Could hormone imbalance be my problem, even after the menopause? Is there anything else I can be doing to lose weight? I would be most grateful for any advice you could offer. Name and address withheld

A1: Once a patient's thyroid function has been shown to be faulty it is up to the doctor to prescribe the amount of thyroxine to achieve adequate correction. The doctor will obviously be guided by your biochemical blood results but will also take into account any physical symptoms - mood, pulse rate, reflex responses, speed of mental reaction, bowel activity, voice, cholesterol and other lipid blood levels etc.

Sometimes an apparently perfect biochemical balance, as judged by the lab blood results, can be achieved but the patient may even so be displaying signs or symptoms of over or under activity of the thyroid. Good medicine is bespoke medicine and every case has to be judged separately.

The fashionable, and widely accepted, medical opinion is that a patient's metabolism is not often, if ever, a factor in weight gain and what matters is that the number of calories is taken in is not greater than the number of calories expended. My own opinion, having been brought up in the countryside, is that this premise flies in the face of all animal management and breeding as practised by farmers and that humans are, even if we don't like to admit it, just animals.

Farmers know that some strains of cattle are good converters and for the same amount of food and exercise put on weight at a commendable rate (if you were a Norfolk bullock being fattened up for the Christmas stock sales your tendency to put on weight would win you red rosettes). They also know that try as they will other animals, that are eating them out of house and home, remain depressingly skinny.

The evidence that we are but animals, so far as weight gain is concerned, is confirmed by studying those races, like the peoples of South Asia, who put on weight readily. They have evolved so that they gain excessive weight quickly during times of plenty so that their fat stores will see them through periods of famine.