FAD diets come and go. The latest is the Fast Diet, also known as the 5:2.
My girlfriend is on this diet and she is thin as a whippet, so I can say that it probably works. But I am pretty sure she's also tried The Zone Diet and the Israeli Diet with weight loss results, because anything that involves cutting kilojoules trims excess fat.
The Fast Diet involves intermittent fasting. Two days a week you severely restrict kilojoules, subsisting on vegies and broths and similar low-kj foods. So it's not for the faint-hearted.
But the benefits include not kilojoule counting the rest of the time - although, obviously, not going crazy with high-fat foods - and, possibly, longevity.
Scientists have long been studying how eating limited kilojoules can add years to our lives.
Research results have been mixed.
In 2009 a study that began in 1989 at the Wisconsin National Primate Research Centre found that kilojoule restriction did extend life in rhesus monkeys.
Scientists found that 13% of the dieting group died from age-related causes, compared with 37% of the control group.
However, a 25-year study published in Nature journal in 2012 was not as rosy.
Rhesus monkeys fed 30% less than control animals did not live longer.
Instead, said scientists, genetics and dietary composition matter more for longevity than a simple kilojoule count.
The research was designed by the National Institute on Aging in Maryland.
Authors of The Fast Diet, Dr Michael Mosley and Mimi Spencer, say the benefits of this eating plan are many fold.
These include a reduced risk of diabetes and improved mood.
The authors also suggest that: "Over a period of weeks you can expect your BMI, your levels of body fat and your waist measurement to gradually fall. Your cholesterol and triglyceride levels should also improve."
So, if you're interested in going on the Fast Diet you simply decide that, two days a week, you will eat no more than 500 to 600 calories or around 2500 kilojoules at most.
Leafy vegetables and steamed vegetables are recommended, as are non-stick pans, low fat dairy, and plenty of fibre.
Soup, especially light broths, are on the menu too while starchy white carbohydrates (bread, potato, pasta) are out.
Generally you only get two meals - breakfast and dinner.
A typical day's menu may include porridge with blueberries and, in the evening, a chicken stir-fry and a piece of fruit.
Or how about a boiled egg and half a grapefruit and, later, a vegetarian chilli.
I know, it's making me hungry too. But the authors assure readers that their body will slowly adjust to this intermittent fasting.
Leading nutritionist Rosemary Stanton has said of The Fast Diet that it may encourage people to gorge on the wrong foods on "feeding days", potentially leading to unhealthy addictions.
Fad diets, she says, are not the answer to weight loss. Rather, healthy meals and daily exercise are the way to go.
One thing The Fast Diet may do is make you aware of just how many kilojoules you normally eat and put you back in touch with your hunger.
Many of us eat on cue and eat portion sizes that are way too large.
But getting a smaller dinner plate and waiting until you are hungry to eat, as well as cutting out high-sugar, high-fat foods and drinks, may pay just as many benefits.