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When Prof Jim Mann was a young man, his father, a GP, was obsessed about people eating too much sugar.

“He’d say ‘you boys’ - referring to me and my friends - ‘you are all eating too much sugar. You’ll be fat and your teeth will fall out’. That was in the 1950s,” he said.

It was also long before John Yudkin’s book, Pure, White and Deadly, proclaimed that sugar was dangerous to health.

However, Yudkin’s science was poor and many other scientists and researchers at the time, including Prof Mann, tended to dismiss his conclusions, although, ironically as it turned out, subsequent research showed his advice was right although much of his science was faulty.

“We know a lot more about the science, the biochemistry and the effect sugar can have on fat metabolism now,” Prof Mann, a leading diabetes researcher, Otago University professor in human nutrition and medicine and director of the Healthier Lives National Science Challenge, said.

For 20 years he has also advised the World Health Organisation (WHO) about the role of nutrition in diseases such as diabetes and heart disease.

While a little bit of sugar occasionally may not be detrimental to most people, the large amounts of it, along with fats and rapidly digested starches, found in many processed and fast foods, not to mention sugar-sweetened drinks, is damaging the health of an increasing number of people.

Apart from adding calories without nutrients and causing weight gain, sugar can be converted into fats, deposited in the liver, causing fatty liver, and have an effect on blood sugar and blood pressure.

The effect of sugar on tooth decay is sometimes overlooked.

“If you look at the picture globally, dental health is most important especially in developing countries where they don’t have good dental care and they don’t have fluoride,” he said.

“In addition to the more obvious consequences of poor dental health, people forget that bad dental disease is an important cause of inability to control your blood sugar if you have diabetes - any chronic infection can do that but dental caries is one of the commonest causes of chronic infection.”

A couple of decades ago the WHO published figures saying that 6% of the global health budget was a consequence of dental caries and it must be worse than that now, he said.

Sugar, saturated fat and rapidly digested starches such as white flour, bread and other baked goods made from it, and white rice, along with ultra-processed food, fast food and sugar-sweetened drinks contribute significantly to obesity, which is a major cause of diabetes and diabetes is now probably one of the main causes of cardiovascular disease.

However, Prof Mann says, it’s important to keep the big picture in perspective when talking about obesity and diabetes.

“People often talk about the risk of Covid overwhelming the health system in a country like New Zealand. However, short of a major epidemic of infectious disease, diabetes is putting a far greater strain on the healthcare system.”

Prof Mann was part of a team which produced ‘‘The Cost of Type 2 Diabetes’’ report, which was presented to Parliament earlier this year.

It says the diabetes problem is on a trajectory to reach even greater epidemic proportions than at present here and overseas in the next 20 years despite being largely preventable, able to be managed effectively and, in some cases, reversed. At present diabetes costs New Zealand just under 0.7% of GDP, about $2.1billion, and is going to rise steeply.

“It’s costing the country an absolute fortune and what is really scary is that people are getting it younger and younger. In the past the onset of type 2 diabetes was typically in the 40s, 50s and 60s. Now it may be diagnosed in 14 or 15-year-olds or even younger in those with a strong family history and sections of the population known to have high rates, but anybody can get it.”

The report goes on to look at the cost-benefit analysis of interventions such as better drugs and better foot care to prevent amputations for people who have diabetes, and also two nutritional and lifestyle interventions for prevention and reversal.

Overseas, putting at-risk people into a lifestyle programme has demonstrated a huge cost-benefit, he said.

Nearly 20 years ago he was one of a team working on the Healthy Eating Healthy Action strategic framework for making major changes to our social and physical environment to make it easier for everyone to eat well, be physically active and attain and maintain a healthy weight.

It was introduced when Helen Clark was prime minister and Pete Hodgson minister of health but it was abandoned by the Key government and never reintroduced, he said.

“It was aimed at young people, not just schools. It was getting to the population through young people, particularly Maori and Pasifika, and the influence young people could have on their families. That is the real issue for me, the population issue.”

The current Healthy Families and Healthy School Lunches programmes were helpful for some but were really just “fiddling around the edges of the real problem”, he said.

“My dilemma - everybody’s dilemma - is how do you get this message across positively without fat-shaming and all that kind of thing? Those are the important issues for the country.”

One exciting recent development in diabetes care is that if people with diabetes lose an appreciable amount of weight in a few months, usually with a formula diet, they often go into remission.

People with Type 2 diabetes weigh on average around 100kg and have been eating unhealthily, but if they can lose about 15kg there’s a good chance they can go off their medication for at least three years or longer, provided the weight loss is sustained on a healthy, balanced diet, he said.

“The thing is it requires support - you need people, family, to support you. You need to have access to decent food, which we do have in New Zealand, and it must be affordable.”

Many studies have shown healthy food is not necessarily more expensive than processed and fast food but it is more costly in terms of time and energy to plan and shop.

“If you are poor and working at four jobs, you just don’t have the time for meal planning. It’s much easier to buy some fish and chips,” he said.

Many lower socioeconomic neighbourhoods don’t have fruit and vegetable shops, but do have a lot of fast food outlets.

Transnational food companies have a big effect on global and local food systems, including marketing unhealthy food and drink to school children.

The analogy with the tobacco industry often comes up in this context, but Prof Mann thinks most of the Big Food industries are behaving more sensibly now.

“It’s not necessarily because they want to but because there is so much pressure on them. I think they’ve stopped rubbishing the fact that sugar isn’t so good for you.”

Nevertheless, the report of a new global study by Newcastle University in Australia released in August this year says that one in five published researchers reported being pressured by funders to delay, change or not publish their findings of health behavioural studies when they are unfavourable to the funders’ interests.