What does scientific research say about added sugar and health?
A scientific research literature review of how added sugar impacts health or how removing added sugar impacts health.
When doing a literature review as a lay-person (who is not conducting future research), it’s best to find a “meta-analysis”. A meta-analysis is when academic researchers or scientists look at all the studies on one topic and evaluate them all based on their methodoly and limitations. No study is perfect and that’s because it’s hard to isolate variables, it’s hard to get a random and diverse mix of study participants, there can be funding limitations, and so on.
A meta-analysis will say that based on all the peer-reviewed studies in this one lane, throwing out all the studies that were way off in terms of bias and limitations, the agreed upon conclusion is X.
Often times, wild and misleading news media outlets will grab onto one study and publish an outrageous headline, “Coffee now proven to cause cancer!” or something similar. It’s important to ignore news media based on the release of just one study in a given area and instead find a meta-analysis that looks at all the studies to see what scientists agree on.
As someone with a Master’s degree in Public Health, when I read a healthy study headline in the news, my first thought is always, “I wonder what the study’s limitations were?” Who did they study and was this population representative of a population at large? Were other biases introduced?
When I was a senior at UC Berkeley, I assisted with data collection at two labs. One was a pest management lab and we looked at alternative pest control for walnuts and pears in the Sacramento Valley. To collect data we went out to the orchards, randomly picked pears or walnuts, then examined them for moth larvae. The other looked at the impact of school garden programs on the health of elementary and middle school students in the Berkeley public school system. To collect data we interviewed young students about what they ate. We had them write it down in a journal every day for a week. So we had to explain how to use the journal, then review the journal with each student at the end.
Which one do you think had the potential for more bias and limitations?
I hope you said the one with the students! Humans are complex! Much more complex than walnuts and moths. For example, when humans know we’re being monitored, we tend to choose healthier foods. And we also lie about what we’ve eaten! Walnuts don’t lie.
So all that is to explain that if you’re trying to evaluate a health claim, find a credible meta-analysis.
Here’s what I found on added sugar and health:
Review of the scientific evidence used for establishing US policies on added sugars (2019)
Body weight. Of the 10 intervention studies that evaluated the effect of increased intake of free sugars on body weight in adults, 6 showed a significant increase in body weight and a 14% to 23% increase in calorie intake with increased free sugars compared with the control. The other 4 studies showed no effect on body weight. On the basis of the meta-analysis of these 10 studies, increased intake of free sugars was associated with a significantly greater body weight.
Cardio-vascular disease. The 2015 DGAC concluded that moderate evidence from prospective cohort studies indicates that higher intake of added sugars, especially in the form of sugar-sweetened beverages (SSBs), is consistently associated with increased risk of hypertension, stroke, and coronary heart disease in adults.
Sugars and health: a review of current evidence and future policy (2016)
This is a great one because it includes a history of sugar production and availability. It also uses and defines the term “free sugar” which is a little easier than the term “refined added sweeteners” but means the same thing.
Type 2 Diabetes. The automation of the process of extracting sugars in the 1900s reduced cost and increased availability of sugars leading to a dramatic rise in consumption, which reached a peak in the 1970s. There are different definitions for sugars not naturally available in foods, and free sugars is the term used by WHO. The epidemiological evidence of the associations between sugars and obesity and type 2 diabetes mellitus is fairly strong and consistent, particularly for sugar-sweetened drinks in adults. The Department of Health in the UK and many other countries have recently updated their recommendations for free sugars as a result of this scientific evidence. In the UK the recommended amount of free sugars is currently 5 % of energy (reduced from 10 %), which is difficult to meet and very different from current British dietary patterns.
The Impact of Free Sugar on Human Health—A Narrative Review (2023)
This one is nuanced! It’s a deep dive and it’s comprehensive. It stresses how difficult it is to isolate variables when studying nutrition. It’s why we can often hear so many contradictory things when get nutrition advice.
“Observational and experimental studies into the impacts of sugar consumption on cognition are vulnerable to the same limitations of food frequency questionnaires and recall bias as described above. Research should also account for alternative macronutrient intake as high-fat diets have been associated with cognitive impairments and dyslipidaemia, and salt is implicated in high blood pressure. Fibre may have a protective effect due to its role in the microbiome. While these factors should be considered in future research, the current evidence strongly indicates a major role for refined sugars in cognitive dysfunction and dementia.”
I’m sure you’re TLDR (too long didn’t read) on this whole study so essentially it’s saying:
there’s mixed results but essentially eating more calories in general is associated with great health risks
eating healthy, nutrition foods like leafy greens and fibrous foods can offset the negative impacts of free sugar
The thing about sugar is that it’s calorie dense but doesn’t make us feel full so it really goes without saying that free sugar adds a lot of calories to our diet but we keep going for more food because we don’t feel satiated.
“Our systematic review and meta-analysis demonstrated that consumption of SSB intake appears to increase the risk obesity and cardiometabolic diseases, being the strongest evidence for type 2 diabetes. Actions are needed to be taken to reduce the SSB intake and its consequences worldwide.”
“The review demonstrated that the effect of fructose-containing sugars on adiposity may be mediated by controlling calories consumed (energy) and that the effect varies among the types of fructose-containing food sources. Excess energy intake at high doses (≥100 g/d) of SSBs, fruit drinks, and mixed sources with SSBs generally leads to increases in adiposity.” (adiposity = body fat)
Essentially saying, people can eat free sugar as long as they keep their total calories low. And this is so true! But hard. And sugar has an addictive quality to it that many other foods don’t.
In conclusion:
It’s tough to say whether sugar itself is worse than just eating more calories than we need BUT sugar is a big reason many of us eat more calories than we need. Eating more calories than we need is associated with type 2 diabetes, heart disease, and other health risks.
Putting this much “free sugar” into so many foods has been a 100 year experiment and it’s not going very well…
