But crazy as it sounds, Unwin has found that most of his diabetes patients who follow this advice are getting their blood sugar back under control, and that some are coming off medication they have relied on for years. Those who are overweight are slimming down.
This might seem like just another controversial fad diet, but a growing number of researchers, doctors and nutritionists around the world are backing it, and reporting their findings in peer-reviewed medical journals. Last month, the National Obesity Forum, a UK body for health professionals involved in weight management, made headlines when it overhauled its advice, telling people to ditch calorie-counting, low-fat foods and carbs in favour of fats.
The recommendations provoked a furious backlash from mainstream scientists and dieticians, but they should concern us all. If the advice is to be believed, starchy food isn't just bad for diabetes, it makes us fat and causes heart attacks. This is analogous to finding that smoking protects people from lung cancer, says David Haslam, an obesity specialist at the Lister Hospital in Stevenage, UK, and head of the National Obesity Forum. "It is terrible," he says. "We have let people down."
For decades, standard dietary advice has been to shun fat and fill up on starchy food like bread, potatoes and rice. We are told this is good for our waistlines and our hearts, and is especially important for anyone with diabetes. Guidelines in the UK, the US and Australia, for instance, tell people to fill around a third of their plates with starchy food. When the UK government agency Public Health England revamped its "Eat Well Plate" earlier this year, it cut added fats (such as oils and spreads) down to a mere 1 percent of the recommended food intake.
Fat first came under suspicion when research early last century found that the arterial plaques that can lead to a heart attack contain the fatty compound cholesterol. Then came several studies showing that heart attack rates were higher in countries where people ate more fat, especially saturated fat from meat and dairy foods. Fat was also deemed the enemy of people wanting to stay slim, since it has over twice the calories, gram for gram, as carbohydrates and protein.
From the 1950s onwards, these ideas crystallised into official dietary guidelines, and the health-conscious started switching to leaner cuts of meat, low-fat milk and swapped butter for vegetable-oil based margarines. And they filled up on starchy carbs.
Yet average body weight has continued to climb, as have rates of associated problems such as type 2 diabetes, culminating in what is now arguably a health crisis. In the UK, US and Australia, around two-thirds of the population are either overweight or obese.
Critics of the idea argue that mainstream nutritional advice is based on decades of research, involving many hundreds of thousands of people, showing that a diet too high in saturated fats is bad for the heart.
And yet in the past few years, a body of literature has emerged to suggest that the question of fat might not be as straightforward as we once thought. For instance, a recent analysis of past studies found that diets lower in saturated fat are not significantly associated with less heart disease or stroke. Another found that the effects of reducing saturated fat depended on what people ate instead; there was a small benefit from replacing it with polyunsaturated fats, but no benefit from replacing it with carbs. The best kind of study is a randomised trial that alters people's diet to see how their health changes. Here too, there is conflicting evidence â€“ some trials show a benefit from reducing saturated fat, while others indicate none or even the opposite.
A high-fat diet could also be concealing other aspects of lifestyle or diet, such as too much sugar or a lack of exercise, which may be the real culprits for heart problems.
It also seems fat is a more diverse food group than it first appeared. Oils from plants tend to be unsaturated fats, liquid at room temperature; we thought of these as "good", unlike saturated fat, mostly found in meat and dairy products and solid at room temperature. But recent studies suggest that dairy fats, which are saturated, do seem to protect people from type 2 diabetes and heart disease.
The role of insulin resistance, the key problem in diabetes, also seems to be a bigger player in heart problems than we thought. One recent study found it is a bigger heart attack risk factor for men than high blood pressure, high cholesterol and being overweight. "We have been focusing on the wrong things," says Aseem Malhotra, a cardiologist at the Lister Hospital, who is a vocal advocate of low-carbing.