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At last. This [news today about low-fat foods could impair ovulation] has been known around the fertility clinics for some years, but has been pooh-poohed by the low weight lobby. The specific dairy fat information is interesting. The connection with women being too light to ovulate, while being within the "ideal weight" guidlines is well known. However clinics have reported that certain women demand clomid rather than increase their weight, despite medical advice that weight gain (not excessive, just enough) is the safer way for their infertility problems, such is the hold of this low fat, low weight, mania on women. This was 12 years ago when I had difficulties (not that particular one I hasten to add) but I am not surprised that it has taken this long for a serious study. Another study overlooked, I think produced by a Midlands university, is the connection between a low fat diet and depression. I just hope some notice is taken this time, but I doubt it. Emaciation is queen! * C.A. Metcalfe, Essex

As you say the association between infertility and low weight has been known about for many years. Another carefully controlled pro-active trial showed that when hyper thin ballet dancers, who are not ovulating or menstruating, had time away from their dancing school, went home and enjoyed steaks and chops their ovulatory periods returned. Likewise during the war many women who had had a poor diet in occupied Europe only found that their cycle returned to normal once they received protein in their diet. My advice to my sons, (which has been ignored!) is that they should marry intelligent milkmaids. The current lack of dairy produce in the diet of girls at or around the start of their periods is likely to cause a serious epidemic of osteoporosis in thirty or forty years time.

This recent study from Harvard is, as you say, and as any doctor would expect, a serious piece of research but its importance will eventually be shown to be entirely dependent on what is meant by a randomised control trial. Women, or men for that matter, who are obsessional about their health very often have other personality problems and the anthithesis of the easy-going relaxed woman who is likely to conceive easily. It is known since time immemorial that tense, stressed, strained women have problems with ovulation and conception. Could this describe the nature of the nurses who were obsessional about having low fat dairy produce and yoghurt? Nor is it certain that a nurses' lifestyle is necessarily representative of that of the population as a whole.

It may be that a demand for low-fat dairy produce and yoghurt is a marker for the very type of personality, whatever their job, that might find it difficult to conceive. Without knowing more about the psyche and the rest of the subject's lifestyle together with their weight and diet including their protein intake it would seem to be difficult to draw firm conclusions from it and it might either be worthless or, even worse, misleading. It does however raise important points for future discussion.

How do I give up chocolate and sugar in general? Amber Long, Glasgow

Don't bother. Chocolate can be an important part of someone's diet. What matters is that the cocoa content of the chocolate should be high. Rather than giving up chocolate I would suggest that you learn to like the rather bitter, black chocolate containing at least a seventy percent cocoa content. Cut back on sugar. Small reasonable quantities are unlikely to rot your teeth or destroy your insulin balance and upset insulin resistance. Remember that doctors must have contributed to the death of tens of thousands of patients with diabetes in their 30s 40s 50s and 60s by advocating a low carbohydrate but high-fat diet. Moderation in all things is usually the answer in life and that includes the numbers of pieces of sugar you put in your tea and coffee. Make certain that your waist measurement is kept below 35 inches, and preferably 33.

I am 60 and reasonably healthy. I have a commuter-type diet, by which I mean I eat on the run and quite often later than I should for the sake of decent digestion. For example, I often pick up a vegetable samosa and tea at 9.30 in the evening at a mainline station in London on my way back to the suburbs. I have given up red wine for Lent. Surely this can't be bad for me? Sally Butcher, Maldon, Essex

Not much good for you either. I myself wouldn't suppose that if I ate a greasy vegetable samosa bought from a mass produced line sold at an outlet of a main line station that I was doing anything more than boosting my calorie intake and blood sugar level after a hard and irritating day in the office. Unfortunately, the story you tell is so very much like that of many commuters. Ideally you should have a good breakfast before you leave for work, but few of us have the time for it. In this office my colleague makes certain that I eat bananas, small packets of apricots, dates and nuts (with the occasional reward of some dark chocolate) for elevenses and at teatime. Rather than always having coffee, we have fruit juices at least once a day. We also try to have fish in some form three times a week, it all helps to dilute the effects of any drinks that are needed after a fairly stressful day at work. (See my article on giving up food or drink for Lent on February 23).

Is it true that vitamin pills give me a five percent greater chance of dying than if I didn't take anything, as reported in today's Times? Peter Harris, Reading, Berkshire

I doubt it. As with the research at Harvard on low fat food, unless one knows a great deal more about the people who were involved in this meta analysis it would be poor science to draw conclusions from the work. Like the Harvard research, but to an even greater extent, this paper has done no more than raise interesting debating points. It must also be remembered that this was a metanalysis from Copenhagen, not a single prospective or even retrospective trial and that the reports we have had in the papers contain none of the details that would enable us to judge the quality of each of the many 47 trials that were chosen for inclusion.