Prof Jim Mann has a personal mission: he wants people to be aware how much sugar they are having, because right now it's almost impossible to tell.
Sugar is hidden in many manufactured foods and drinks, some of them quite unexpected.
Prof Mann, of the human nutrition department at the University of Otago, is a member of the committee of the World Health Organisation (WHO) which released its draft recommendations about sugar in March.
It has been attracting a lot of coverage, some of it misunderstood, he says.
''People have made WHO sound like this terrible sort of ogre, the sugar police,'' he said.
''It's very important to get this in perspective. The draft recommendation said there is strong evidence that people shouldn't increase their sugar intake and most people should decrease it,'' he said.
The second recommendation is that free sugars should be less than 10% of the total energy intake.
The third recommendation is conditional; that it should be considered whether the recommended upper limit for sugar intake should be reduced to 5% of the total energy intake, which equates to about 25g or six teaspoons in an average diet of 2000 calories.
It was conditional because it wasn't absolutely certain yet although there was good evidence dental caries were at their lowest when free sugar was below 5%, Prof Mann said.
''The recommendations are based on dental caries, which is a terribly important global problem that people forget. It's not just a few bad teeth that can be prevented by going to the dentist occasionally.
"It involves 6%-20% of the health budget worldwide and that is independent of the effect of fluoridisation, which reduces dental caries. It's up there with the major killing diseases in terms of health expenditure,'' he said.
Besides dental caries, sugar was strongly implicated in obesity and all the problems that came with it, and there was some evidence that sugar might have an independent effect on blood pressure and lipids, Prof Mann said.
''The WHO is saying if you want to do something about dental caries and all the things that go with obesity, definitely make sugar less than 10% of your total calorie intake, and if you can, go even lower than that.
''My bottom line is sugar is not the cause of obesity, but it's a contributing factor to obesity and if you want to do something about obesity you have to do something about sugar as well as other things.''
The other things include reducing energy-dense foods, reducing fat and the quantity of food eaten, and doing more exercise.
The WHO specifies the reduction of ''free sugars'', which means sugars added by manufacturers, cooks and consumers - sugars in things like biscuits, sweets, breakfast cereal, sauces, stirred into your tea or coffee or sprinkled on your porridge.
It includes not only sugar in white, brown, raw and other forms, but also honey, syrups like maple, agave and corn syrup, as well as fruit juices and fruit concentrates, but not whole fruit.
''Clearly if you are having fruit juice you are having a better product than if you are having cordial or soft drink, because there is no benefit in cordial whereas in fruit juices you are getting some other things.
"But if you want to take into account dental caries, obesity and possibly some of the other independent effects of free sugars, then you are really talking about all free sugars, and fruit juice, honey and maple syrup are no different from the others,'' he said.
''If you want to put maple syrup in your muffins, do it because it tastes nice. Nobody's saying you shouldn't, but don't kid yourself it ain't sugar.''
Prof Mann said sugar in whole fruit was different from sugar in fruit juice, partly because of the quantity.
You'd normally eat only one or maybe two oranges, but it might take five or more to get a glassful of orange juice and you would get the sugar from all of them.
Also important was that in fruit, sugar was packaged in the cell walls that had to be broken down first, so it was digested more slowly and absorbed more slowly so the liver was able to deal with it from a metabolic point of view.
If you were eating a lot of free sugar it would be in your bloodstream within minutes.
Dried fruit was an intense source of sugar and it was easy to eat a lot of it so you got a lot of sugar, but it did have the cell walls intact to some extent.
''There's very little research on it but if someone were to say to me what's better to eat, sugar or dried fruit, I'd say dried fruit, but I'm sure it's got the dental caries effect because you are chewing that sugar round in your mouth.''
• Some people say sugar is addictive and although Prof Mann says there is some evidence for it, he considers the jury is still out.
He suspects people become habituated to sugar rather than strictly addicted.
''Babies like sweet things. It's natural. I think 'addictive' is too strong. It probably depends on your personality, if you have a potentially addictive personality,'' he said.
''I've got a very sweet tooth but I'm definitely not addicted to sugar because I find it relatively easy to say no.''
Research is ongoing and as reliable new evidence is found, opinions and recommendations change.
Back in the late 1960s, John Yudkin, author of Pure, White and Deadly, a book claiming sugar was a poison, was widely derided for his flawed science, although he achieved a popular following.
According to Prof Mann, Yudkin's science was still considered flawed and although he was probably not quite right in terms of ''pure white and deadly'', now we actually had some science that said we should restrict sugar.
''It's interesting for me because I was one of the people who rubbished Pure, White and Deadly. I debated with him on prime-time BBC television and he told me when I grew up I might have more sense. His science was totally unsubstantiated but in part he was right.''
Then the fat message took over as a major factor in cardiovascular and other lifestyle diseases and the sugar debate was more or less forgotten - not that the fat message was wrong, Prof Mann said.
Manufacturers introduced low-fat products and added lots of sugar to boost the flavour.
These days there is talk about introducing a tax on sugary beverages, something Prof Mann thinks could be a good thing.
''Nobody needs sugary beverages; it's just rubbish food. I think for some sections of the population it [a tax] would be quite helpful. Pacific and other youth, for example, drink enormous quantities of this, and if you made it really expensive that would be good because they don't need it.
''The advantage of taxing sugary beverages is it has no downside for anyone except the manufacturers, there are no health disadvantages and the extra money the Government would make out of it could be put to use in other areas of health,'' he said.
''The only real downside, though I can't see any government doing it, is it highlights one thing, and one thing isn't going to solve obesity.
''It's not sugar, it's a combination of things, eating too much high-sugar, high-fat, energy-dense food, and lack of exercise.''
Tips to reduce sugar
Prof Jim Mann's personal mission is for people to know how much sugar they are having, because right now they don't.
Food labelling is difficult to understand and often misleading. Whether you aim to have no more than 5% (about 25g or six teaspoons) or the currently recommended 10% (around 50g or 12 teaspoons) of your daily calories from sugar, you need to be aware of the hidden sugars in manufactured food.
Sugar is hard to avoid. In ingredients lists look for sugar and its aliases: brown sugar, fructose and crystalline fructose, high-fructose corn syrup, invert sugar, rice/corn/maple/malt/golden/palm syrup, corn sweetener, maltose, sucrose, glucose, molasses, syrup, dextrose, honey and raw sugar.
Check the nutrition label for sugar percentage and amount per serving, although serving sizes can be misleading.
Prof Mann came across a yoghurt drink recently that had a Heart Foundation tick.
Checking the small print on the back showed the package contained three servings and at that quantity the amount of sugar would not be too bad per serving.
However, the servings were very small, even a child would drink the whole pack and that would be your 10% of sugar in one drink, he said.
• A product labelled ''low fat'' often means it has been bulked out with sugar - read the nutrition label carefully.
• The average can of soft drink contains about 35g of sugar, about 9 tsp. Avoid soft drinks and energy drinks.
• Breakfast cereals can contain up to 38% sugar; many, even those promoted as healthy, can contain about 18% sugar: a bowl of breakfast cereal may contain about 14g of sugar. Switch to a lower sugar one or make porridge and add you own sugar if needed.
• Tomato sauces, BBQ sauces, relishes and chutneys can contain between 25% and 39% sugar - a tablespoon of ketchup can contain 7g.
• Canned baked beans and spaghetti can contain about 5% or 6% sugar.
• Many ready-made pasta sauces, soups and canned products contain 3%-4% sugar.
• Sweetened yoghurt, flavoured milk and other dairy products usually have high amounts of sugar. Choose a plain, unsweetened one and stir in your own fruit.
• Drinking chocolate can contain about 6 tsp of sugar per serve. Use cocoa, sweeten it yourself.
• Cakes, biscuits and even ''healthy'' oatmeal and muesli bars often contain 25%- 35% or more sugar.
• Many breads, including the healthier wholegrain ones, contain 3%-4% sugar. Read the labels carefully and if you think this is too much, make your own bread.
• ''Lite'' or reduced sugar products are appearing on supermarket shelves. Check the ingredients and nutrition labels.
• You can often reduce sugar in cooking. It's rarely needed in main courses, vegetables, breakfast dishes or snacks. Most fruit is naturally sweet and doesn't need much, if any, added sugar.
When making jam, instead of the traditional proportion of 1kg sugar to 1kg of fruit, Prof Mann recommends using 600g of preserving sugar, which has added pectin, to 1kg fruit. Boysenberry jam made this way is delicious, he says.
In baking, sugar affects volume, moisture, texture and colour of cakes and biscuits as well as adding sweetness. However, many recipes have more sugar than necessary and too much sugar can obscure the flavour of other ingredients, such as chocolate. Some people say you can reduce the sugar in most recipes by a quarter or even half without much noticeable difference. You can use a mashed ripe banana, fruit puree or dried fruit instead of some of the sugar, although this might affect the texture. Sweet spices such as vanilla, cinnamon, nutmeg, mint and angelica, or orange or lemon zest can intensify the flavour.
Experiment: your cake or biscuits might not be quite the same but that's not necessarily a bad thing.
