Achieving and maintaining a healthy body weight through good food choices and an active lifestyle is recognised by both the Australian Dietary Guidelines and the Eating and Activity Guidelines for New Zealand as crucial in attaining optimal health and wellbeing.
Being overweight and obese is defined by the body mass index (BMI). BMI checks if a person is a healthy weight for their height and is calculated by dividing weight (kg) by height in meters squared.
The BMI ranges:
18.5 or less = underweight
18.5 - 24.99 = healthy weight
25 - 29.99 = overweight
30 or more = obese
Current evidence suggests people with a BMI of less than 18.5 or higher than 25 are more likely to die prematurely of a health-related issue than those with a BMI within the defined healthy weight range. BMI however is not a perfect measure. It can misclassify those with a muscly build and does not distinguish where fat deposits are stored. Abdominal or central adiposity is an indicator of increased risk of certain diseases.
Overweight and obesity trends in both Australia and New Zealand are concerning. In the latest National Nutrition Survey, 63% of Australian adults were overweight or obese. This was a similar statistic to New Zealand where 65% of adults are overweight or obese. Obesity itself has increased in the last decade across all age groups and both genders. Being overweight or obese increases a person's risk of cardiovascular disease, some cancers, type 2 diabetes and premature death.
Research into the causes and risk factors of obesity and the 'best diet' for weight loss continues. However, for the majority of the population it is well accepted that energy consumption, in excess of energy expenditure leads to increased body weight. Because sugars are ingredients in many popular foods, their role in obesity has been widely investigated. The research to date indicates that there is no direct relationship between sugar intake and obesity.
Sugars, as with other carbohydrates, fats, protein and alcohol, contribute to overall energy intake. The question still remains whether energy intake or energy expenditure is the main influence on obesity and more, well-designed research into this area is required.
A sole focus on sugar may not have the intended effect of reducing obesity levels in the population if other energy sources are not also considered. For example systematic reviews of the research have shown no unique role for sugars having a detrimental effect on body weight. Rather, that reducing sugar consumption may lead to weight loss (or a reduction in weight gain), if there is an energy deficit. It is clear that the same could be said for any other energy-providing nutrient in the diet. Cutting down on all sources of energy, including sugars, when they're consumed in excess, is therefore an evidence based approach.
In addition, sugar sweetened beverage (SSB) intake is often studied as a unique marker of sugar intake. Evidence from recent randomised controlled trials suggests a possible link between SSBs and body weight, largely due to their additive effect on total energy intake, though reviews show not all studies have consistent findings. According to new research SSB intake has been in decline. The same can be said for total sugar consumption and apparent consumption of refined sugar.
A study published in the European Journal of Nutrition found that apparent consumption of refined sugar decreased by 23% since 1980 – the same time period in which obesity rates tripled. This data is supported by the most recent National Nutrition Survey which found total sugar consumption had declined by 2% over the last 16 years. In New Zealand intake has declined by 9% between 1997-2008.
In the absence of just providing excess energy the research explores glycemic index, glycemic load, satiety of liquid calories and displacement of other nutrients as potential mechanisms for promoting obesity.
Fructose in particular is suspected by some for the increase in obesity in western countries. The biological basis for this theory is founded in how our body metabolises fructose and glucose differently. However scientific evidence is limited to animal studies and studies in at-risk humans fed excessively unrealistic quantities of fructose. Evidence of a relationship with normal moderate intakes of sucrose in healthy populations is lacking. In fact, a recent review on fructose found that calories from fructose will cause weight gain in the same way as calories from any other nutrient.
Displacement of nutrients was the topic of a systematic review by Gibson. Required vitamin and mineral needs were meet across a broad range of sugar intakes. Observed negative associations between added sugar intake and micronutrient density reflects more the overall diet quality rather than the amount of sugar consumed. A small amount of sugar may encourage the consumption of nutritious foods.
Research is currently focussing on the role of gut health and the health of the microflora in our gut on obesity. Trials in this area and the impact of diet of gut bacteria are predominantly animal based. As this area is explored more, further updates and information will be provided.
Regardless of dietary source, eating too many kilojoules (calories), without the right amount of activity to burn it off, will lead to weight gain. Because people tend to like sweet foods and drinks, some argue that they can be easily over-eaten, leading to excess energy intake, though consumption of sweet foods and drinks alone, when all other dietary factors are controlled for, is not associated with weight gain.