Imagine you are eating a meal; what do you eat first? Whether you are at a buffet, a nice sit-down restaurant, or cooking at home, meals typically have a combination of foods that can be roughly divided into proteins, fats, starchy carbohydrates, and fibrous vegetables. There is little to no debate that early treatment or prevention of postprandial hyperglycemia is important for health, especially in those with type-2 diabetes (T2D). Recently, researchers publishing in Diabetes Care asked whether the order in which a meal was consumed would influence the metabolic response to it in 11 T2D men and women.

After a 12-h overnight fast, subjects consumed an isocaloric meal (628 kcal: 55 g protein, 68 g carbohydrate, and 16 g fat) with the same composition on 2 separate days, 1 week apart. During the first visit, the food order was carbohydrate (ciabatta bread and orange juice), followed 15 min later by protein (skinless grilled chicken breast) and vegetables (lettuce and tomato salad with low-fat Italian vinaigrette and steamed broccoli with butter); the food order was reversed a week later.

The results clearly show that food timing within a meal plays an important role in glucose metabolism. The reduction in postprandial glycemia (PPG; -73.5%) was comparable to that seen with pharmacological agents such as metformin, and the reduction in insulin (-48.5%) suggests an effect on insulin sensitivity as well. Unfortunately, this study only tells us that these outcomes occur and does not provide any insight into the mechanisms behind the benefits.

Notably, this was the first study to document these effects in the American population with a Western-like meal (and not a bad one by any means). Until now, this concept had only been explored by Saeko Imai of Osaka Prefecture University, Japan. The first publication evaluating the effect of “vegetable before carbohydrate” involved 15 T2D patients consuming a small test meal of white rice, sliced cabbage, and tomato (340 kcal; 62g CHO & 2g fiber; 8g FAT; 5g PRO) after a 12-hour overnight fast. The patients ate either rice first or vegetables first, chewing more than 20 times each bite with a 10-min interval between rice and vegetables. Eating vegetables first clearly reduced the blood glucose and insulin response.

What is more impressive is that a second portion of this study recruited 333 T2D outpatients to receive education involving “eat vegetables first” or no education (control group) and had a follow-up period of 30 months. In the education group only did HbA1c decrease from 8.3 to 7.1 %, and this went hand-in-hand with reductions in daily energy intake and consumption of rice, fruits, oils, sweets, and beverages. On the other hand, intake of fibrous vegetables increased.

The second publication by Imai appeared in the Asia Pacific Journal of Clinical Nutrition in 2013 and aimed to determine whether educating T2D patients to “eat vegetables before carbohydrate” was as effective on long-term glycemic control as a traditional exchange-based meal plan. Overall, 101 patients were randomized to receive instructions on either a simple meal plan that involved eating vegetables before carbohydrates (VBC) without taking into account energy intake, or a traditional exchange-based meal plan (EXB) that used the food exchange system to focus on energy intake. HbA1c decreased significantly in both groups initially, were significantly lower in the VBC group compared to the EXB group at 6, 9, 12 and 24 months. This is despite no significant differences in BMI or blood lipids throughout the 2-years.

The third and final publication is novel in that it tested these effects in healthy and T2D subjects. Over the course of a day, the subjects consumed three test meals providing a 30 kcal/kg (17% PRO; 25% FAT; 58% CHO) and 21g of dietary fiber. These meals were composed of rice or bread, meat or fish, and 500g of vegetables (tomato, spinach, broccoli, and radish, etc.) The subjects ate the first dishes of vegetables for 5 min, then the main dish for 5 min, and consumed rice or bread for 5 min successively within a 15 to 20 min total eating time for each meal, and vice versa.

The levels of SD, MAGE, large amplitude of glycemic excursions (LAGE), mean 1-h postprandial glucose (PPG), mean incremental area under the glucose curve_0-3h (IAUC_0-3h), and mean incremental glucose peak (IGP) were all significantly reduced when the participants ate vegetables before carbohydrates compared to the reverse regimen in both subjects with T2D and NGT.

Although only a handful of studies have looked into the effect of meal timing on glycemic control, the results are consistent and promising. Not only does it appear to be an effective method for short- and long-term benefits in persons with T2D, but the effects appear to extend to healthy individuals as well. We may be able to speculate that the effects are owed to the slowing of gastric emptying or gut-peptide effects, but more research is needed to know for sure.

Currently, the focus for hyperglycemic management is on the total amount of carbohydrate consumed. The approach of eating vegetables and protein before carbohydrates supports the concept of emphasizing food choices, what to eat first, and how to eat. Depending on how much the person likes vegetables, they may not even be hungry for the carbohydrates by the time they get around to them.

I wonder how much of an additional impact including some vinegar with the protein and veggie portion of the meal would have on the glucose response to the carbohydrates that come later.