COMMENT: Sitting on my bookshelf, among the other old diet and recipe books, is one of my favourite volumes: The Complete Woman Book of Successful Slimming.
This book was published in 1966 and contains photos of lithe ladies with perfectly coiffed hairdos exercising in modest black leotards. There's also some lavish, for the time, colour spreads of recipes in all their parsley-sprinkled glory, and advice on corsetry and "clothes that help you cheat" and look slimmer.
The thing that interests me most about this, though, is the diet advice, which is actually a a low-carb diet.
Cutting carbs is "the best of the modern methods", say the authors, and their meal plan lists most carbohydrate-containing foods in a complicated points system, to be limited to a certain number.
Meat "of any description (including canned meat, bacon, poultry, offal, liver sausage)" can be eaten freely, however, as can aspic, almonds, sour pickles and salt. A half-pint of milk is to be consumed every day.
Apart from the exercise gear and the quaint food, though, this is not much different from many modern low-carb diets.
What this shows me is that in the world of diets, nothing is really new. Just as in fashion, diet trends come and go, and they tend to borrow from the past, even when offering a revolutionary new science sell.
It makes me smile to see the proponents of some current low-carb diets claim they have discovered something new. The fact is, we have heard almost everything before. We just tend to forget, and when it cycles around again, like goldfish, we're newly excited.
This is not to say that nutrition science does not progress. It's widely acknowledged now that all carbohydrates are not equal; that there are some (refined, white) carb-containing foods we'd be better off never eating again, and that many of us would probably do well to eat less carbohydrate than we might have in the past.
But the idea that this one thing - low-carb eating, or the keto diet, or low-carb/high-fat, or any other current variation - is the answer, the one and only way of eating that will save us all, is clearly flawed.
And even when they say "It's not a diet! It's a lifestyle!", we should know a diet when we see one.
I Googled "carbophobia" to see what I could find on the current prevailing fear of potatoes and pasta. What I got, surprisingly, was a book of that name, written back in 2005, when the Atkins Diet (another low-carb diet) was at its peak. The book railed against the low-carb trend. It sold well at the time, but the lasting impact seems negligible.
In nutrition, things are never really so black and white. Nutritionists now would generally acknowledge that a well-planned, plant-based low-carb diet will work well for some people. But it's by no means the only way of eating to be healthy.
• Niki Bezzant is editor-at-large for Healthy Food Guide www.healthyfood.co.nz