Though there is an element of preaching in what the author gives us in this book, he makes a genuine attempt to be informative rather than moralistic. Now in his mid-80s, Dr Norman Lazarus is a retired medical doctor and is still involved in research on the ageing process.

The book is directed at people in the post-50 age group who find themselves with more personal time because of their changed life circumstances. Many such adults do not lead an active life and are overweight, as a result of career or other earlier choices. Lazarus identifies three elements that people need to be aware of when speaking about ageing - the Healthy Ageing Trinity, he calls them. They are exercise, food and the mind.

He deals with the first two in great detail. About the mind, he insists that he is not talking about cryptic crosswords or sudoku or memorising verse - activities that this reviewer enthusiastically recommends - but rather stresses the role that physical exercise and proper diet play in keeping the mind active and functioning.

As hominoids, we evolved to be hunter gatherers, he says; any excess fat that our body may collect is merely evolution's way of dealing with a bad hunting season and ensuing hunger. He admits that in his middle years, he had a minor problem with his weight, something he realised when buying a pair of trousers at an outlet in London's Regent Street. He noted the gently raised eyebrow of the shop attendant when he asked for a 32 or 33-inch waist. He left in a huff when it turned out that he needed a 36-inch. That was the beginning of his determination to monitor his weight, a check that would not be via bathroom scales but would have him on penal diet until he was able to fit again into a 32-inch waist, a situation that still obtains now that he is in his middle-80s.

The longest chapter in the book deals with the problem of over-eating. Americans have in recent times classified obesity as a disease, an opinion he dismisses. For the British NHS, it is a serious problem and one that may at some time in the future, lead to government regulations about diet and exercising before the health services can be called upon.

The author strongly advises against reading books on diet and admits that he never watches food programs on television. Interestingly, he does not mention the modern tendency of some sensitive citizens to claim discrimination if someone suggests they may be overweight.

From some period in our 30s, we are ageing, a phenomenon that involves all our body parts, and, he says "the only known effective therapeutic intervention is physical activity", a point he drills home again and again. The research studies that he quotes involve subjects in their 60s, 70s or 80s.

There is a danger with a book like this that the reader may feel he/she is about to be the subject of an extensive sermon with much finger-waving. Lazarus manages to avoid this, mainly by his simple and clear statements. Healthy ageing, he writes, "is the process of developing and maintaining the functional ability that enables well-being in older age... Ageing is not a disease". A compelling read.