ULTRA-PROCESSED FOODS, GI AND GL

Ultra-processed foods do not have a high GI or GL. Minimally processed foods are not low GI.

I’m going to be frank with you. I’m sceptical of the theory that ultra-processed foods (UPF) are a major factor in the epidemics of obesity and other chronic diseases (1). Indeed, I think their very definition lacks scientific credibility because it’s based on the idea that when we produce food in a factory (as opposed to a home kitchen) using economies of scale, they are somehow different in a slightly sinister way. And when we add substances such as emulsifiers or colours or flavours (but not preservatives) and package them in an appealing way, we have created the ‘devil’s food’. If not evil, perhaps too palatable, more tempting, more likely to cause us to overeat than the food prepared at home?

Now, if you had a grandmother like mine (and she lived to 106 years of age), she knew how to tempt me every day of the week. I recall huge meals served on enormous plates. There was no shortage of vegetables or meat, or butter, sugar or eggs. The UPF theory also suggests that the food industry produces food that is more appealing than the average restaurant…but I wouldn’t agree. If you’ve heard of Julia Child (2), you’ll know that French recipes prepared in the home require some skills but are well worth the effort. French restaurants have more Michelin stars than any other country (3). But guess what…it’s true that French women don’t get fat…they have one of the lowest BMIs (Body Mass Index) in Europe, along with the women of Switzerland and Belgium (4). They also happen to have the highest consumption of chocolate (a UPF of course) in the world.

One hypothesis that could be true is the ultra-processed food is ‘different’ because it has a higher glycemic index (GI) or load (GL) than minimally or moderately processed foods. Recently my colleagues at the Universities of Arizona and Sydney put that idea to the test by a careful analysis of the GI and GL of almost 2000 foods in the latest edition of the International Tables of GI and GL (5). The findings surprised even us.

Firstly, we manually assigned a processing level to every single food in the database according to the NOVA classification:

• Group 1: Unprocessed or minimally processed foods.
• Group 2: Processed culinary ingredients.
• Group 3: Processed foods.
• Group 4: Ultra-processed foods

These groupings can be a little ‘woolly’ (ambiguous even among scientists), so we used a consensus-based approach and also carried out sensitivity studies. Firstly, we found no difference in GI and GL across processing levels. In fact, the UPFs tended to have lower rather than higher GI values (average GI of 49) compared with the average GI of 54 in minimally processed foods.

Secondly, we looked at GI values within the various categories of foods (think fruits, vegetables, dairy….). Again, in most categories there were no differences according to processing level. But there were 2 exceptions. Within the grains group, GL was significantly lower in the UPF foods and within vegetables they were higher. Addition of fats and sugars to UPF foods might explain a lower GI and GL, while instant potatoes may be the explanation for a higher GI of the UPF level among vegetable foods.

These findings are important. They infer that if there are any potential adverse consequences of ultra-processed foods, it is unlikely to be related to their glycemic index or GL.

Like others, I don’t think there is value in using processing level as a guide to dietary choices (7). Like Rachel Carson’s Silent Spring, I am concerned that the UPF theory may have unintended consequences. Dr Carson’s warning was prescient in relation to endocrine disrupting substances that have a long half-life, like phthlates and PFAS. But she also created several generations that have ‘chemophobia’, where any substance that is not familiar or is man-made is a chemical and must be harmful. The fear of vaccination among some people can be traced to this ‘fear of chemicals’.

I also fear a continuing rise in eating disorders caused by the demonisation of yet more foods. Surely by now, we know fats, sugars and other carbohydrates do not need to be demonised in order to moderate consumption.

Read more:

1. Monteiro and colleagues. Does the concept of “ultra-processed foods” help inform dietary guidelines, beyond conventional classification systems? YES. The American Journal of Clinical Nutrition, 2022.
2. Julia Child
3. Luxury Gold. This Country Takes the Crown for the Most Michelin-Starred Restaurants in 2024.
4. Ng and colleagues. Global, regional, and national prevalence of overweight and obesity in children and adults during 1980-2013: a systematic analysis for the Global Burden of Disease Study 2013. Lancet. 2014.
5. Atkinson and colleagues. International tables of glycemic index and glycemic load values 2021: a systematic review. Am J Clin Nutr. 2021.
6. Basile and colleagues. Food processing according to the NOVA classification is not associated with glycemic index and glycemic load: results from an analysis of 1995 food items. The American Journal of Clinical Nutrition, 2024.
7. Astrup and colleagues. Does the concept of “ultra-processed foods” help inform dietary guidelines, beyond conventional classification systems? NO. The American Journal of Clinical Nutrition, 2022.

Emeritus professor Jennie Brand-Miller held a Personal Chair in Human Nutrition in the Charles Perkins Centre and the School of Life and Environmental Sciences, at the University of Sydney until she retired in December 2022. She is recognised around the world for her work on carbohydrates and the glycemic index (or GI) of foods, with over 300 scientific publications. Her books about the glycemic index have been bestsellers and made the GI a household word.