News Briefs includes four fructose studies published in the last year (three of them in recent weeks). We didn’t intend to focus on fructose this issue, but with all the heated debate about sugars (and in particular fructose) and obesity at present, we felt made the decision to run them all, as we felt that GI News readers would be keen to see the latest science on a topical issue that often generates more heat than light. We are sure that you'll agree that it's vital to get the science right and the dogma off the table to have any chance of coming up with solutions (note the plural) to the obesity epidemic.
For weightloss, a moderate natural fructose diet superior to low-fructose diet.
In Food for Thought, Dr Arya Sharma reminds us that there is very little evidence from high-quality intervention studies that attempting to restrict sugar consumption would have the desired effect on obesity or anything else. In fact, there are very few high quality intervention studies at all regarding sugar and fructose consumption and the effects on health. This recent randomised, 6-week pilot study published in Metabolism from Magdalena Madero and colleagues provides a useful addition to the literature. The researchers report that for weightloss, an energy-restricted, moderate natural fructose diet was superior to an energy restricted, low-fructose diet. The 131 obese participants were placed on low-fructose (less than 10 grams a day) diet or moderate natural fructose diet (50–70 grams a day with natural fruit supplements). The diets consisted of 55% carbs, 15% protein and 30% fat. All participants lost weight, but those in the moderate natural fructose group lost nearly 50% more (4.19 ± 0.30 kg) than participants in the low fructose group (2.83 ± 0.29 kg). The percentage of body fat dropped in both groups but the difference wasn’t statistically significant. In terms of changes in the measured health parameters (blood glucose, blood pressure, blood fats, insulin resistance) there were no significant differences between the groups. Concluding, they write: ‘for weightloss, a moderate natural fructose diet was superior to a low-fructose diet. Such a diet may offer greater benefits than other energy-restriction diets, as it does not entail the restriction of total carbohydrate intake and hence may be more sustainable.’
Commenting on this study, Dr Alan Barclay says that while it appears to be about fructose, when you read through it you see that the authors state that the reason why the moderate fructose (high fructose by Australian standards) diet caused greater weight loss than the low fructose diet was because it has a lower GI: ‘patients in the very low fructose diet had a higher glycemic index and glycemic load’.
Is fructose being blamed unfairly for obesity epidemic? Or do we just eat and drink too many calories?
Dr John Sievenpiper
In a systematic review and meta-analysis of more than 40 published studies on whether the fructose molecule itself causes weight gain in Annals of Internal Medicine, researchers from St. Michael's Hospital conclude that: ‘Fructose does not seem to cause weight gain when it is substituted for other carbohydrates in diets providing similar calories. Free fructose at high doses that provided excess calories modestly increased body weight, an effect that may be due to the extra calories rather than the fructose.’
In 31 ‘isocaloric’ trials they reviewed, participants ate a similar number of calories, but one group ate pure fructose and the other ate non-fructose carbohydrates. The fructose group did not gain weight. In 10 ‘hypercaloric’ trials, one group consumed their usual diet and the other added excess calories in the form of pure fructose to their usual diet or a control diet. Those who consumed the extra calories as fructose did gain weight. However, all that could mean is that one calorie is simply the same as another, and when we consume too many calories we gain weight, said the lead author, Dr John Sievenpiper.
‘Fructose may not be to blame for obesity,’ he said. ‘It may just be calories from any food source. Overconsumption is the issue.’ Participants in the studies examined by Dr. Sievenpiper ate fructose in the form of free crystalline fructose, which was either baked into food or sprinkled on cereals or beverages. The studies did not look at high fructose corn syrup, which has been singled out as the main culprit for weight gain as it is only 55 per cent fructose, along with water and glucose. Dr. Sievenpiper said the majority of studies they examined were small, of short-duration and of poor quality, so there is a real need for larger, longer and better quality studies.
Prolonged fructose intake not linked to rise in blood pressure
Eating fructose over an extended period of time does not lead to an increase in blood pressure, according to a new study published in Hypertension. It found that despite previous research showing blood pressure rose in humans immediately after they consumed fructose, there is no evidence fructose increases blood pressure when it has been eaten for more than seven days. In fact, researchers led by Drs David Jenkins and John Sievenpiper observed a significant decrease in diastolic blood pressure – the measure of blood pressure when the heart is relaxed between contractions– in people who had eaten fructose for an extended period of time. ‘A lot of health concerns have been raised about fructose being a dietary risk factor for hypertension, which can lead to stroke, cardiovascular disease, renal disease and death,’ said Vanessa Ha, lead author of the paper. ‘However, we wanted to determine whether fructose itself raised blood pressure, or if the apparent harm attributed to fructose was simply because people are eating too many calories. For example, we know that people are consuming more soft drinks than ever, but is it the fructose, the extra calories, or possible other factors that are adding to their illnesses?’
The study looked at the effect of all sources of fructose, including natural and crystalline. In the systematic review and meta-analysis, Ha and colleagues pooled the results of 13 controlled feeding trials which investigated the effects of fructose on blood pressure in people who had ingested fructose for more than seven days. The 352 participants included in their analysis ate an average of 78.5g of fructose every day for about four weeks. Ninety five percent of all people in the US consume less than 87 g per day.
Fructose and BGLs
First of all, despite what this story says, we are not advocating that you add pure fructose to your meals instead of your usual sweetener – many factors need to be taken into consideration when making that decision and we recommend you discuss the issue with your health professional first. The point of studies like this is to get the science right and the dogma off the table. In this small meta-analysis of 6 controlled feeding studies published in the British Journal of Nutrition, Dr John Sievenpiper and researchers from St Michael's Hospital found that contrary to concerns that fructose may have adverse metabolic effects, there is evidence that a small ‘dose’ (around 10g or 2 teaspoons) of fructose can actually lower the glycemic response to a high GI meal without adverse effects on fasting insulin or body weight. In their conclusion, they call for larger and longer trials to confirm these results.
Is ‘fat’ the sixth taste?
Dr Russell Keast
Researchers in Australia and the US have found that along with sweet, sour, salty, bitter and umami there seems to be a sixth taste – ‘fatty’. Deakin University researchers reported in the British Journal of Nutrition that our tongues can detect a sixth taste – fat. They also found that people with a high sensitivity to the taste of fat tended to eat less fatty foods and were less likely to be overweight. They suggest that training our taste buds’ sensitivity to fat is a potential way to reduce overweight and obesity. Deakin’s Dr Russell Keast explains that: ‘people insensitive to fat taste tend to consume more energy because their body does not tell them to stop eating. What is measured in the mouth reflects the body’s response to fats,’ he said. ‘Those who are insensitive to fat taste do not get the fullness signals. So, when consuming a fatty meal, a healthy weight person would start to feel full and stop eating and the gap between meals would also be extended. However, those who are insensitive to fat taste do not feel full and therefore keep eating and the gap between meals is also reduced. In our study we also found that the people with less sensitivity to fat taste ate significantly greater quantities of butter, meat and dairy. This finding leads us to believe that specific foods groups and perhaps different types of fats are associated with decreased sensitivity to fat in foods.’
According to researchers at Washington University School of Medicine writing in the Journal of Lipid Research, genes probably do play a part. They found that people who made more CD36 protein could easily detect the presence of fat – in fact, those who made the most were eight times more sensitive to the presence of fat than those who made about 50 per cent less of the protein. ‘The ultimate goal is to understand how our perception of fat in food might influence what foods we eat and the quantities of fat that we consume,’ says Prof Nada A. Abumrad. ‘What we will need to determine in the future is whether our ability to detect fat in foods influences our fat intake, which clearly would have an impact on obesity.’