Type 2 diabetes (T2D) is a chronic condition caused by the body’s inability to properly use or produce enough insulin, causing sugars to build up in the blood. T2D is also a significant global health burden; recent studies estimate that around 536 million adults are affected by the condition as of 2021. This is predicted to rise to 783 million by the year 2045, with associated healthcare costs expected to surpass $1,054 billion.
Dietary patterns, alongside physical activity and other lifestyle factors, have been identified as a significant contributor to developing diabetes in large observational studies. But exactly how does what you eat affect your diabetes risk?
In this article, we summarize some of the hot research topics and major discoveries in scientists’ exploration of the link between food and diabetes risk.
Ultra-processed foods may increase type 2 diabetes risk
Ultra-processed foods (UPF) are the “new kid on the block” in terms of dietary research. The concept, first defined by a research team from the University of São Paulo, is best explained through the NOVA food classification scale, also introduced by the same research group.
NOVA classification
Group 1 foods are completely unprocessed or natural foods, including seeds and fruits, animal products (milk, eggs, unprocessed cuts of meat), fungi and algae.Group 2 foods are “processed culinary ingredients”, such as oils, butter, sugar and salts derived from Group 1 foods or natural processes such as pressing and churning.Group 3 foods are traditional processed foods; most have 2–3 ingredients and are recognizable as modified versions of Group 1 foods, for example, tinned fish, fruits in syrup and cheeses. Group 4 foods are UPF, described as “not modified foods but formulations made mostly or entirely from substances derived from foods and additives, with little if any intact Group 1 food.” Examples would include soft drinks, sweet or savoury packaged snacks, reconstituted meat products and pre-prepared frozen meals.
Investigating the potential health effects of this ultra-processing is a growing field of research. To date, several studies have connected UPF to changes in diabetes risk.
A recent, major The Lancet Regional Health – Europe study from researchers at the University of Cambridge and Imperial College London investigated the relationship between the degree of food processing (as defined by the NOVA scale) and T2D risk. Analyzing UPF intake and health outcomes for 311,892 individuals from 8 European countries over approximately 11 years, they found that every 10% increase in the amount of UPF in a person’s diet is linked with a 17% increase in T2D risk – but this risk can be lowered by consuming less-processed foods instead.
“People who consume ultra-processed food probably are at increased risk of diabetes, as this observational study finds, but it is not possible to disentangle the effects of poor diet and degree of food processing without robust randomised studies,” commented Dr. Gavin Stewart, reader in interdisciplinary evidence synthesis at Newcastle University, who was not involved in the study, to the Science Media Centre.
“The problem is that ultra-processed foods are not consumed in isolation. They are usually part of a high-fat, high-sugar diet and may also be associated with lifestyle factors that have deleterious health impacts. The authors attempt to disentangle these factors where they can with sensitivity analyses testing modeling assumptions and make appropriately nuanced conclusions, but without better (randomized) evidence, we don’t understand the causal links.”
Researchers have also conducted studies to attempt to unravel the effects of consuming specific types of UPF.
In an Australian study of different soft drinks, the researchers found that drinking just a single can of artificially-sweetened soft drink daily may increase the risk of developing T2D by 38%. For regular sugar-sweetened soft drinks, T2D risk also rose, but only by 23%.
Even after adjusting for body weight, the connection between artificially sweetened drinks and T2D remained strong, suggesting a potentially direct effect on metabolism. This may have important implications for public health policy, as lead study author Prof. Barbora de Courten, of Monash University and RMIT University, explained: “We support measures like sugary drink taxes, but our study shows we also need to pay attention to artificially sweetened options. These are often marketed as better for you; yet may carry their own risks. Future policies should take a broader approach to reducing intake of all non-nutritive beverages.”
In another study aiming to unravel the effects of processing, researchers from Aarhus University and the Albert Einstein College of Medicine looked at the association between the intake of potatoes prepared by different methods (boiled, baked, mashed and French fries) and T2D risk. The data came from 205,107 adults enrolled in 3 major US cohort studies carried out between 1984 and 2021. Across these studies, a total of 22,299 T2D diagnoses were recorded during almost 40 years of follow-up.
After adjusting for other lifestyle and dietary factors, they found that for every 3 weekly servings of potato, the rate of T2D increased by 5%. But for every three weekly servings of French fries, T2D rate increased by 20%. Substituting baked, boiled or mashed potatoes with whole grains was also found to lower the rate by 4%, while replacing French fries lowered the rate by 19%. However, the observational nature of the study again limits any conclusions around causality.
Could a diet rich in whole foods protect against diabetes?
Aside from UPF, scientists are also keen to study other dietary choices and evaluate their effects on T2D risk – for better or worse.
Beyond processed snacks, observational studies have also shown associations between the consumption of processed meats and higher diabetes risk. A recent study published in the Lancet Diabetes and Endocrinology found that the habitual consumption of 50 grams of processed meat a day – equivalent to 2 slices of ham – was associated with a 15% higher risk of developing T2D in the next 10 years.
The study, which drew on data from 1,966,444 adults across 20 countries, also noted that the habitual consumption of 100 grams of unprocessed red meat a day – equivalent to a small steak – was associated with a 10% higher risk of T2D.
“Our research provides the most comprehensive evidence to date of an association between eating unprocessed red meat and processed meat and a higher future risk of type 2 diabetes,” said senior study author Nita Forouhi, a professor of population health and nutrition at the University of Cambridge’s MRC Epidemiology Unit. “It supports recommendations to limit the consumption of processed meat and unprocessed red meat to reduce type 2 diabetes cases in the population.”
Conversely, scientists studying the low-carbohydrate plant-based diet have suggested that this way of eating could benefit those already diagnosed with T2D. One study, led by researchers from the Harvard T.H. Chan School of Public Health, found that following a low-carb diet comprised primarily of plant-based foods was significantly associated with lower risk of premature death among people with type 2 diabetes. The study examined 34 years of health data from 7,224 women participating in the Nurses’ Health Study and 2,877 men participating in the Health Professionals Follow-up Study, all of whom developed type 2 diabetes after those studies began.
“While avoiding refined and highly-processed carbohydrates has been widely recommended to lower the risk of developing type 2 diabetes, our study provides the first empirical evidence on how low-carb diets can help manage the progression of existing diabetes,” said lead study author Yang Hu, then a research associate in the Department of Nutrition.
Researchers are also examining whether certain components within foods might be used to prevent diabetes.
Sorghum is an abundant grain that requires fewer resources to grow than other crops, but it is more commonly used for animal feed than for human consumption. But researchers from Hokkaido University and the University of Sydney recently discovered that it contains a wealth of lipids that could have beneficial health effects.
Using nontargeted lipidomics, the team profiled the lipids present in six different sorghum cultivars, finding novel bioactive lipids known as fatty acid esters of hydroxy fatty acids (FAHFAs). These are “unique lipids that were known to have anti-diabetic and anti-inflammatory properties”, according to the researchers.
“With its gluten-free properties and rich supply of essential fatty acids, sorghum provides a solution to nutritional gaps, particularly for individuals with gluten sensitivities or those seeking natural dietary interventions for chronic health conditions as well as lifestyle-associated metabolic diseases,” said associate professor Siddabasave Gowda of Hokkaido University’s Faculty of Health Science and Graduate School of Global Food Resources, who led the research. “The study underscores the increasing demand for functional foods that combat lifestyle-related diseases like diabetes and heart disease while promoting overall well-being.”
Separately, researchers at the University of Gothenburg have shown that a chemical compound found in broccoli sprout extract could be useful in tackling T2D and prediabetes. In one study, the team discovered that taking large doses of sulforaphane extracted from broccoli sprouts can reduce hepatic glucose production and improve glucose control in patients with T2D. More recently, the same research team confirmed that sulforaphane can also improve blood sugar levels in people with prediabetes – a precursor to T2D where blood sugar levels slowly rise due to impaired insulin production.
Diabetes and the gut microbiome
So processed foods, red meat and high-carb diets can increase T2D risk, while plant-based whole food diets may have a protective effect. But how exactly does food affect your risk of developing diabetes?
Having the odd candy bar or steak here and there is unlikely to have a significant effect. But habitually eating high amounts of refined carbohydrates, sugary drinks and processed meats can result in chronic levels of high blood sugar, as the body processes starchy and sugary foods into glucose to provide energy to cells. Over time, chronically high blood sugar can negatively affect the body’s ability to use insulin properly, leading to insulin resistance and a significantly higher risk of developing T2D.
However, new research suggests that food could be affecting T2D risk in another way – by directly altering the gut microbiome.
In 2024, researchers from Brigham and Women’s Hospital, the Broad Institute of MIT and Harvard, and the Harvard T.H. Chan School of Public Health published a paper in Nature Medicine detailing the largest and most ethnically and geographically comprehensive investigation to date of the gut microbiome in people with type 2 diabetes (T2D), prediabetes and healthy glucose status.
Where prior studies of the gut microbiome and its role in T2D had been too small and varied in study design to draw significant conclusions, they had observed a general trend linking changes in the gut microbiome – the collection of bacteria, fungi and viruses that inhabit our intestines – to the development of T2D. In the Nature Medicine paper, the researchers affirmed that specific species and strains of bacteria were linked to changes in the functioning of the gut microbiome and a person’s risk of T2D.
“We believe that changes in the gut microbiome cause type 2 diabetes,” said study author Fenglei Wang, a research associate in the Harvard T.H. Chan School of Public Health. “The changes to the microbiome may happen first, and diabetes develops later, not the other way around – although future prospective or interventional studies are needed to prove this relation firmly.”
“If these microbial features are causal, we can find a way to change the microbiome and reduce type 2 diabetes risk,” he added. “The microbiome is amenable to intervention – meaning you can change your microbiome, for example, with dietary changes, probiotics or fecal transplants.”
Separately, other research teams have already linked certain foods with changes in the gut microbiome that may affect T2D risk. One mouse study led by scientists at Columbia University found that dietary sugar can alter the gut microbiome and set off a chain of events that leads to metabolic disease, pre-diabetes and weight gain. While the human and mouse microbiomes are dramatically different, the researchers say their findings underscore the “complex interaction between diet, microbiota and the immune system” and how this interaction “plays a key role in the development of obesity, metabolic syndrome, type 2 diabetes and other conditions.”
Another study led by Kristina Petersen, associate professor of nutritional sciences at The Pennsylvania State University, found that consuming 2 ounces of pistachios each night for 12 weeks resulted in significantly different stool microbial community profiles in people with prediabetes than those who ate a carbohydrate-based bedtime snack.
“Pistachios seem to be able to meaningfully shift the gut microbial landscape in adults with prediabetes, especially when consumed as a nighttime snack,” Petersen said. “These microbiome changes may offer other long-term health benefits – potentially helping to slow the development of type 2 diabetes or to reduce systemic inflammation – which we hope to explore in future research.”
Food and diabetes risk is a continually evolving area of scientific research; with diet being so closely tied to other lifestyle factors such as physical activity and household income, it can be extremely challenging to disentangle the effects of a particular food or food group and determine its impacts on the gut microbiome, diabetes risk or, more broadly, on human health.
To reduce your risk of developing T2D, Diabetes UK – a major campaigning and research charity – advises eating a balanced diet with plenty of fruit and vegetables and fewer processed foods, as well as moving more and maintaining a healthy weight.