Study: Eating order is important

reference

Imai S, Kajiyama S, Kitta K, et al. First consumption of vegetables, regardless of eating speed, has a significant reducing effect on postprandial blood glucose and insulin in young healthy women: randomized controlled cross-over trial.Nutrients.2023;15(5):1174.

Study objective

To investigate the effect of eating speed and eating order on postprandial blood glucose levels in healthy women

Key to take away

Consuming plant-based and protein-containing components of a meal significantly reduces the glycemic impact.

design

This study used the same group in a crossover design where all participants ate identical meals at three different eating speeds and eating orders.

Participant

21 female students from Kyoto Women's University took part in this study between April and July 2022.

Three of the 21 participants did not complete the study. The average age of the 18 women who completed the study was 21.3 years, the average BMI was 19.6 kg/m2, and the HbA1c was 5.2 ± 0.3%.

None of the participants were pregnant, had eating disorders, had metabolic diseases, followed specific diets, or were taking medications or supplements that would affect blood sugar, insulin, or lipid levels.

None of the participants had type 2 diabetes mellitus (T2DM) or a family history of this disease.

intervention

Identical meals were eaten on three different days, one week apart, with different eating habits on each occasion. Two meals were eaten slowly, either vegetables first or carbohydrates first. The third meal was eaten quickly with vegetables first.

All meals consisted of vegetables (tomatoes and broccoli with sesame oil), fried fish and boiled white rice. The slow meal was carefully timed and extended to 20 minutes. The quick meal was eaten in half that time.

Evaluated study parameters

Blood samples were collected at 0, 30, 60, and 120 minutes after the meal and tested for blood glucose, insulin, triglycerides (TG), and free fatty acids (FFA). The area under the curve (IAUC) was calculated for glucose and insulin.

Primary outcome

The study aimed to investigate whether the speed of eating or the order of meals had an influence on postprandial glucose or insulin levels.

Key findings

Eating the vegetable portion of the meal first and eating slowly had a significant impact on postprandial blood glucose at 30 and 60 minutes compared to all other eating habits.

30 minutes postprandial:

1. langsames Essen mit Kohlenhydraten zuerst: 7,09 ± 0,34 mmol/L,

2. schnelles Essen mit zuerst Gemüse: 5,94 ± 0,24 mmol/L (P<0,05).

3. langsames Essen mit zuerst Gemüse: 5,53 ± 0,25 mmol/L, (P<0,01)

60 minutes postprandial:

1. langsames Essen mit Kohlenhydraten zuerst: 5,88 ± 0,34 mmol/L

2. schnelles Essen mit Gemüse zuerst: 4,95 ± 0,18 mmol/L

3. langsames Essen mit zuerst Gemüse: 4,97 ± 0,16 mmol/L (P<0,05)

Note: After 60 minutes, there was no difference between slow and fast eating among those who ate vegetables first.

Postprandial insulin concentrations were significantly lower when vegetables were eaten first than when carbohydrates were eaten first.

transparency

The study was funded by Grants-in-Aid for Scientific Research KAKENHI (20K11569) from the Japan Society for the Promotion of Science (JSPS). The authors declare that they, their immediate families, and any research foundations with which they are affiliated have received no financial payments or other benefits from any commercial entity related to the subject matter of this article. The authors declare that, although they are part of a department that receives funding from a pharmaceutical company, they have not currently received funding for this study and that this does not alter their compliance with all journal policies regarding the sharing of data and materials.

Implications and limitations for practice

Over the last decade, a new approach to dietary glycemic control has entered the medical literature. The new approach assumes that the order in which we eat different foods in a meal plays a significant role in the resulting blood sugar levels - far more than we might have suspected. This study is part of a series of reports helping to improve our understanding.

Eating carbohydrates on an empty stomach has a far greater impact on blood sugar than eating the same foods during or after a meal.

Alpana Shukla et al. published an earlier study on the timing of food composition in 2019. In their study, participants were served a meal of grilled chicken, steamed vegetables, and a salad with vinaigrette on two different days. On one of these days they ate a standard size ciabatta before dinner. Another day they saved the bread until they had eaten everything else. Blood sugar levels dropped by 40% when vegetables or proteins were eaten first. In other words, blood sugar increased by 40% when the bread was eaten first.¹

An even earlier study led by Saeko Imai was published in 2014 and reported a significant effect of simply consuming vegetables before carbohydrates in a group of Japanese patients with type 2 diabetes, both acutely and over a 2.5-year follow-up period. These studies were notable because they used continuous glucose monitoring systems developed in 1999 that enabled the collection and analysis of this complex data. The attenuation of hyperglycemic episodes was more pronounced in diabetics than in diabetics without diabetes.²

In a 2018 study, Nishino et al. reported that saving carbohydrates for last—after meat or vegetables—lowered blood sugar levels in healthy Japanese volunteers without diabetes.³

The idea that fast eating and fast eating are associated with a higher risk of obesity first emerged in a national survey in New Zealand in 2011.⁴ In 2014, a Japanese survey (N=56,865) found that fast eating is linked to metabolic syndrome.⁵ A smaller 2012 survey found that fast eating was associated with T2DM in men (N=2,050).⁶

There may be a reason why this strategy has received more attention in Japan than in the United States, becoming a recognized nutritional strategy for treating diabetes there.⁷ Japanese and other people of East Asian descent often have delayed insulin secretion, which is about half that of people of European descent.⁸It is therefore not clear whether the magnitude of the blood sugar difference is as dramatic in other populations.

The most likely explanation for the improvement in postprandial blood sugar levels is that the vegetable's high fiber content slows the digestion of subsequently consumed carbohydrates. There's another possibility in this current study: The sesame oil in which the vegetables were cooked may have triggered the release of incretin hormones, which increase insulin secretion and delay gastric emptying.⁹

Nevertheless, this is such a simple and easy-to-implement health intervention strategy that it is our job to educate patients, especially diabetics, about its possible potential benefits.¹⁰

We should eat vegetables or protein before eating carbohydrates. When we do this, the speed of eating has little impact. By vegetables we mean recognizable vegetables that, when cut into pieces, are still whole enough to name. Researchers have tried adding pureed vegetables to rice to achieve a similar improvement without finding any benefit—which, unfortunately, probably means that the tomato sauce on a slice of pizza doesn't matter.