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A new study shows that a potato-based diet does not disturb blood sugar control in patients with type 2 diabetes mellitus (T2DM).
It is a well-known fact that patients with type 2 diabetes mellitus (T2DM) need to avoid eating a carbohydrate-rich diet, such as one containing many potatoes and other high glycemic indexes (GI) food, because it can increase blood glucose levels.
However, according to a new study in the October 2020 issue of Clinical Nutrition, researchers from Australia and the United Kingdom have found that people with T2DM do not necessarily have to avoid potatoes (more specifically, white potatoes), as consuming potatoes does not affect blood sugar control, especially at night. Based on the results of a rigorously controlled clinical trial at La Trobe University in Australia, glycemic index (GI) is not observed to be an accurate surrogate marker for an individual’s glycemic response (GR) to foods consumed during an evening meal. Moreover, the study found out that patients had a better glycemic response at nighttime after eating a mixed meal with peeled white potatoes (high GI) than an isoenergetic and macronutrient-matched mixed meal, which included basmati rice, a low GI carbohydrate food.
In the study, 24 participants with T2DM were provided with a fixed breakfast and lunch meal (50% carbohydrates, 30% fat, and 20% protein). Afterward, they were randomly assigned to one of the four dining options, such as peeled white potatoes (test meal) cooked in three different ways (boiled, roasted, and boiled, then cooled, then reheated once again) or basmati rice (control meal). Afterward, the participants repeated the experiment, taking a 9-day break between each trial, to cycle through all three test meals and the control meal. Blood samples were collected regularly (both immediately after meals and every 30 minutes after 2 hours). Aside from that, a continuous glucose monitoring (CGM) device was also used to track changes in blood glucose levels while the study participants were sleeping.
Results showed no significant differences between meals in glucose response (GR) of patients following dinner with any of the potato meals or basmati rice. Furthermore, the participant’s nocturnal GR was more favorable after eating any of the high GI potato dishes than low GI basmati rice.
Dr. Brook Devlin from the Australian Catholic University stated that “the findings are contrary to that of observational research and traditional dietary guidance that has led some to believe that potatoes are not an appropriate food of choice for patients with T2DM.” Rather, the findings show that high GI food, such as potatoes, can be consumed safely as part of a healthy evening meal by people with T2DM without affecting their GR negatively. Potatoes also deliver vital nutrients in relatively few calories, which is essential for patients with T2DM.
Although the glycemic index (GI) is widely used by nutritionists worldwide, the study results show that GI is not an appropriate tool for understanding how a meal impacts glycemic control in patients. It should be used as a measurement guide for food consumed during isolation, such as controlled clinical trials. Dr. Devlin added that people rarely eat food in isolation; however, the rigorously controlled study had a more realistic sense of daily food consumption due to food pairing or mixed meals.
The study design followed a randomized crossover among participants while measuring blood glucose levels immediately after meals and overnight to determine the impact of high GI food on glycemic response. Though the study was deemed a success, one of the study’s limitations was the short duration of observation, which means that the long-term impact of potatoes on GR is yet to be determined. Aside from that, the baseline GR of study participants was only assessed for one evening meal. However, the researchers concluded that since potatoes are vegetables, they are sustainable, affordable, and nutrient-dense, all of which can play “an important role in modern diets irrespective of patient’s metabolic health status.”
Practice Pearls:
- Glycemic index (GI) is not an accurate surrogate marker for an individual’s glycemic response (GR) to foods consumed during an evening meal.
- Some patients with T2DM had a better nocturnal glycemic response when they ate a mixed meal with peeled white potatoes compared to a low GI carbohydrate food such as basmati rice.
- A potato-based diet does not disturb blood sugar control and hence it can now be safely given to patients with type 2 diabetes.
Arjay Mendoza, PharmD Candidate, University of Colorado Denver Skaggs School of Pharmacy and Pharmaceutical Sciences