There are many aspects of conventional dietary ideology that I don’t agree with. Not because I look for conflict and disagreement, but because so many concepts within dietary ‘conventional wisdom’ are simply not supported by the evidence (and, in fact, may be harmful).
One common theme we see crop up in dietary dogma centres around calories, and the need to reduce calorie intake if we want to lose weight. Fat is obviously in the firing line here again, and so maybe sugar. Outside the soft drinks industry, there is quite a lot of support for the idea that sugary soft drinks, say, are not good for those seeking to maintain a healthy weight. The conventional line is that artificially sweetened diet drinks are better. Even soft drink manufacturers such as the Coca Cola Company draw our attention to their artificially-sweetened offering for those concerned about weight.
However, the promotion of artificially sweetened drinks for weight control is not something I can support in good conscience. Leaving the potentially toxic nature of artificial sweeteners aside, there evidence linking artificial sweeteners and weight gain and also other issues including metabolic syndrome (‘abdominal obesity’ and raised markers for cardiovascular disease and type 2 diabetes) and type 2 diabetes.
The major findings from the scientific literature and their implications were discussed recently in a review paper in the journal Trends in Endocrinology and Metabolism, authored by behavioural neuroscientists Professor Susan Swithers from Purdue University in the US [1]. Professor Swithers has a special interest in the role of artificial sweeteners in health, and has previously published several papers on the subject.
In the review, Professor Swithers cites a recent study in which sugar-sweetened beverages were at east partially replaced with artificially sweetened ones (or water) [2]. These substitutions did improve certain health markers including waist circumference, but no more so than ‘attentional control’ (essentially, being conscious of the dietary choices we make). Also, those practising attentional control or replacing sugary drinks with water saw an improvement in fasting blood sugar levels, while those drinking artificially sweetened drinks did not. I wrote about this study here.
Professor Swithers cites another study, this one in children, which found that drinking one artificially sweetened drink a day compared to one sugar-sweetened drink each day led to weight being 1 kg lower after 6 months, as well as lower levels of body fatness [3]. However, this study did not test how artificially sweetened drinks fared against water. Professor Swithers points our attention to a review that concludes that the evidence in children is ‘mixed’ [4].
Also, in her review, Professor Swithers cites many studies that link the drinking of artificially sweetened drinks to increased risk of, among other things, obesity, metabolic syndrome and type 2 diabetes in humans. Now, a potential explanation here, as she points out, is that individuals seeking to control their weight may be more likely to choose artificially sweetened drinks rather than sugary ones. In other words, whatever weight issue exists is ‘causing’ the increased intake of artificially sweetened drinks, rather than the other way round.
However, she also cites evidence that shows that when people are followed over time, in individuals who essentially start off at the same weight, those opting for artificially sweetened drinks are at increased risk of weight gain compared to those who, say, do not opt for these beverages. The same is true for type 2 diabetes.
These findings suggest that the idea that heavier people are more likely to opt for artificially sweetened drinks does not adequately explain the associations between these drinks and obesity and type 2 diabetes. This does throw up the possibility that artificial sweeteners have the potential to actually cause obesity and other chronic health issues. It should perhaps be borne in mind that none of the epidemiological studies where people were followed over time found artificially sweetened beverages to be associated with improved health outcomes.
Professor Swithers goes on to describe mechanisms which might explain any ability artificial sweeteners have to drive obesity and other health issues. She writes about how when we eat something with, say, sugar in it, the body responds in a way which is geared to metabolising whatever it is we’ve eaten, and that calories should be registered appropriately by the body through signals that adjust hunger to ensure we do not overeat. However, as Professor Swithers points out, there is evidence in animals that the consumption of artificially sweetened drinks disrupt these mechanisms, which in turn may lead to weight gain and other problems.
In one study, rats were fed with either saccharin or sugar-sweetened yoghurt in conjunction with their normal diet [5]. Compared to those eating sugar-sweetened yoghurt, the rats eating saccharin-laced yoghurt consumed more calories and got fatter too. The authors of this study (one of whom is Professor Swithers) concluded that:
…using artificial sweeteners in rats resulted in increased caloric intake, increased body weight, and increased adiposity [fatness].
The authors also added that:
These results suggest that consumption of products containing artificial sweeteners may lead to increased body weight and obesity by interfering with fundamental homeostatic, physiological processes.
In other study, this one from earlier this year, rats were split into three groups, each of which was given unlimited amounts of standard rat food (chow) and water [6]. The groups were also given access to yoghurt sweetened with either saccharin, aspartame or sugar (sucrose).
Rats eating the artificially sweetened yoghurt ate more chow than those eating the sugar-sweetened yoghurt. In the end, overall calorie intakes were the same. This suggests that when reduced-calorie foodstuffs are consumed, there can be a natural drive to seek those ‘missing’ calories elsewhere.
What was also interesting about this study, though, was that the rats consuming artificial sweetener gained weight at a rate faster than those eating the sugar. But the calorie intakes were essentially the same, meaning that change in weight could not be explained by differences in food intake.
Interestingly, it was noted in the previous study [5] that rats experienced some boost in their temperature after eating sugar-sweetened food that was not present after eating saccharin-sweetened food. This suggests that consuming calories from sugar boosts the metabolism in a way that artificial sweeteners may not.
Professor Swithers’ review paper is balanced and evidence-based, and concludes (quite rightly, I think) that we should be cautious over the use of sweeteners, including those that don’t contain calories.
Shortly after this study was published, someone sent me a link to an article in the Daily Mail (a tabloid newspaper in the UK) regarding the safety of artificial sweeteners here. The article, entitled ‘Sweeteners are not bad for you: Take the scare stories about diet drinks and sweets with a pinch of salt, experts say’, focuses on Professor Swithers’ review, and includes these quotes from Catherine Collins, chief dietician at St Georges Hospital in London, UK.
Sweeteners have either zero calories or are very low in calories that aren’t absorbed anyway, so are effectively zero calorie.
So the suggestion that these products are no better at preventing weight gain or diabetes, or that they in fact cause them, is unfounded, as the accepted scientific evidence demonstrates.
However, I’m not as happy as Catherine Collins to dismiss Professor Swithers’ review, particularly if this involves quoting calorie-based based dogma and ‘accepted scientific evidence’ that is not specified. Of course, it’s easy for our quotes and the science to not be represented fully in a newspaper article.
We should give Catherine Collins the benefit of the doubt, I think. It might be that she is aware of a great body of research which effectively dismantles Professor Swithers’ cogent and wide-ranging review, and provides good evidence (say, from randomised controlled trials) that artificial sweeteners are, indeed, effective aids to weight control. If she has this evidence, then no doubt she will provide it here or elsewhere.
References:
1. Swithers SE. Artificial sweeteners produce the counterintuitive effect of inducing metabolic derangements. Trends Endocrinol Metab. 2013 Jul 3 [Epub ahead of print]
2. Tate DF, et al. Replacing caloric beverages with water or diet beverages for weight loss in adults: main results of the Choose Healthy Options Consciously Everyday (CHOICE) randomized clinical trial. Am J Clin Nutr. 2012;95(3):555-63
3. de Ruyter JC, et al. A trial of sugar-free or sugar-sweetened beverages and body weight in children. N Engl J Med. 2012;367(15):1397-406
4. Fowler SP, et al. Fueling the obesity epidemic? Artificially sweetened beverage use and long-term weight gain. Obesity (Silver Spring). 2008;16(8):1894-900
5. Swithers SE, et al. A role for sweet taste: Calorie predictive relations in energy regulation by rats. Behavioral Neuroscience. 2008;122(1):161-173
6. Feijó Fde M, et al. Saccharin and aspartame, compared with sucrose, induce greater weight gain in adult Wistar rats, at similar total caloric intake levels. Appetite 2013;60(1): 203–207 [hr]
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