Ultra-Processed Foods Have a Lower Glycemic Index and Load Compared to Minimally Processed Foods

OBJECTIVES: Ultra-processed foods (UPFs) make up the majority of calories in the US diet. Glycemic index (GI) and load (GL) are measures of the quality and quantity of carbohydrates in food based on their effect on blood glucose post consumption. Diets high in UPFs and GI/GL are both associated with numerous chronic metabolic diseases. Therefore, this study sought to examine the GI and GL of foods assigned to different food processing groups. It was hypothesized that GI and GL would be lowest in minimally processed foods (MPF) compared to processed (PRF) and UPF (with no difference between PRF and UPF) for all food items and food groups. METHODS: GI and GL values produced by healthy/normal individuals for 2,205 food items were collected from published sources. Food items were then coded by processing levels determined by the NOVA Classification. In addition, food items were coded into eight groups (i.e., Beverages; Beans, Nuts, & Seeds [BNS]; Dairy; Fats & Sweets; Fruits & Fruit Juices; Grains; Meat Poultry & Fish; and Vegetables). Hierarchical linear modeling was used to determine significance with an alpha of 0.05. RESULTS: The effect of food processing on GI (p < 0.001) and GL (p < 0.001) was contrary to the hypothesis as the mean GI and GL were highest for MPF: GI (MPF: 56 ± 20, PRF: 53 ± 19, UPF: 50 ± 18), GL: (MPF: 18 ± 11, PRF: 16 ± 13, UPF; 12 ± 8). Among food groups, there was no interaction between food processing and GI (p = 0.084), but an interaction for GL was found (p < 0.001). Moreover, the direction of difference in GL was inconsistent among food groups: BNS (MPF: 6 ± 4, PRF: 9 ± 5, UPF: 10 ± 5), Dairy (MPF: 5 ± 5, PRF: 3 ± 0, UPF: 8 ± 6), and Grains (MPF: 23 ± 9, PRF: 21 ± 15, UPF: 13 ± 9). CONCLUSIONS: Across all analyzed food items, UPF had a lower GI and GL compared to MPF and PRF (GL only), with mixed findings among food groups. Surprisingly, ultra-processing of grains suggests improvement of glycemic responses, perhaps by the addition of protein, fat, and sugars. These results suggest that the negative health outcomes associated with consumption of UPF may be due to other unhealthful aspects (e.g., energy density, food additives, and increased palatability), not higher GI and GL. FUNDING SOURCES: AJB has received the 2021–2022 Graduate Completion Fellowship from the School of Life Sciences, Arizona State University.