Type 2 diabetes (T2D) is increasing worldwide, but the rise is especially fast in sub-Saharan Africa. With complex differences related to ancestry and sex, as well as lifestyle influences including exercise and diet, tackling diabetes requires a combination of population-level strategies and more personal targeted approaches.
The OPTIMA project–featuring STIAS fellow Tommy Olsson from Umeå University, and the principal investigator Julia Goedecke from the South African Medical Research Council, and colleagues–aims to support this goal by identifying ethnic- and sex-specific biomarkers for the early prediction of T2D. These biomarkers will be linked to dietary patterns to develop culturally appropriate prevention strategies.
OPTIMA is a long-term collaboration between researchers in Sweden, South Africa, and Germany, with study sites in Sweden, South Africa, Germany and Ghana, respectively.
Why diabetes is rising
“Sub-Saharan Africa has the highest global rate and highest increases in T2D – this is set to double in the next 50 years,” said Goedecke. “South Africa has an estimated prevalence of 9%. It is the second-leading cause of death overall and the first in women. Worringly, up to 70% of adults are estimated to be undiagnosed.”
“Increasing T2D basically follows the obesity pandemic,” explained Olsson. “Obesity is defined as a Body Mass Index (BMI) of over 30 kg/m2 – in many countries obesity affects over 50% of the population.”
And it’s costing a fortune. “Health expenditure for treating T2D is high and rising,” continued Olsson. “In 2024 an estimated $1000 billion was spent on diabetes treatment and its complications including stroke, myocardial infarction, kidney failure and blindness.”
Type 1 vs Type 2 diabetes
Insulin is necessary for the transport of glucose from your bloodstream into your cells, where it is used for energy.
Type 1 diabetes is an autoimmune disorder where immune cells attack the insulin-making cells destroying the body’s ability to make insulin. It occurs in all ages but the ratio between type 1 and type 2 diabetes is higher among children and young adults. People with type 1 diabetes always need insulin treatment.
In type 2 diabetes–the most common type of diabetes–the body can make insulin but doesn’t use it properly due to an insensitivity to insulin, “insulin resistance”. If there is not enough insulin being produced, glucose is not transported into cells leading to high glucose levels. There are five subtypes of T2D some of which are related to a more pronounced insulin resistance, others associated with less insulin production.
The early stages of T2D (“prediabetes”), is often characterised by a compensatory increase in insulin production to overcome insulin resistance and maintain normal glucose levels, leading to hyperinsulinaemia – very high insulin levels.
Differences between populations
The causes and progression of T2D are not the same everywhere.
“South African women of African ancestry have higher insulin resistance and hyperinsulinaemia than women of European ancestry–even when they are not overweight”, said Goedecke. High-calorie, high-carbohydrate diets can worsen these high insulin levels, which may increase the risk of obesity and diabetes.
They researchers are now testing whether hyperinulinaemia, rather than insulin resistance alone, may be the main driver of T2D in African populations, especially African women.
Treatment including lifestyle changes
Olsson emphasized that weight loss now is considered one of the most effective treatments for T2D, alongside medications such as metformin, SGLT-2 inhibitors and GLP-1 agonists.
“There is good evidence that long-term remission from type 2 diabetes is possible with weight loss alone,” he said. “One landmark study showed that 15 kg of weight loss resulted in remission for 86% of participants after one year.”
Importantly, on a societal level, increased physical activity can be a key component in avoiding weight increase. “Sitting burns very little energy, just standing uses up to three times more”, said Olsson.
We are what we eat–and where we store fat
Goedecke’s research in the Middle-Age Soweto Cohort (MASC) looked at typical eating patterns. The overall diet included 30% plant-based foods, 17% animal-based foods and 11% foods high in vitamin C, calcium and sugar (mainly tea and fruit juices). The staple diet of the South African population is high in processed carbohydrates, and this impacts on obesity more in women than men. “42% of South African women overall are living with obesity“, she added.
However, where the fat is stored makes a difference. Fat stored around the inner organs, known as visceral fat, is strongly linked to higher insulin resistance, and also fatty liver. Women of African descent tend to have less visceral fat than their European counterparts – they are more “pear” than “apple” shaped. These differences may affect diabetes risk and how preventative strategies should be designed. Connected to this, the current waist-measurement cut-off used to signal increased diabetes risk in women is 80 cm. However, Goedecke noted that this guideline comes from studies on European populations, and may not be accurate or suitable for African women.
What OPTIMA hopes to achieve
By studying proteins and metabolites in blood samples, researchers aim to identify biological markers that differ by ethnicity and sex, in order to improve early prediction for type 2 diabetes in African and European populations. They plan to find dietary markers that can show how eating habits influence diabetes risk. This knowledge will be used to develop practical, affordable, personalised prevention strategies and will test how acceptable these strategies are within different communities.
Questions on medications and policy
Speaking about newer and generally very effective drugs for treating obesity and T2D–such as this targeting the GLP-1 or the combined GLP-1/GIP receptors, like Ozempic and Mounjaro–Olsson noted that they are currently very expensive. This may change once patents expire and more competing drugs enter the market. However, these medications must be combined with intensive behavioral therapy to achieve and maintain the best results. In addition, long-term data on their safey and effectiveness are still limited.
When asked about the role of governments, Goedecke stressed the need for stronger policies promoting healthier diets, especially for children. “Fruit and vegetables are perceived to be expensive, while cheaper foods like maize meal, white rice and pasta are common among low-income households.” However, reducing the intake of luxury items such as alcohol, cigarettes, sugar sweetened beverages and excess meat could help healthier foods more affordable.
“A recent world-wide study has shown that about 10% of all cases of diabetes are due to sugar-sweetened beverages,” added Olsson.