Effects of different types of meals on postprandial glycaemia in healthy subjects

Introduction

Currently, continuous glycaemic monitoring systems are used primarily for diabetic patients. Most include a biosensor that connects to an app on the phone. The most popular CGMs measure glucose concentration in the interstitial fluid every 1 or 5 minutes, providing the patient with 288 or 1440 measurements in a day [1]. Continuous glucose monitoring systems show an all-day glucose profile, giving the user a detailed view of fasting as well as post-meal glycaemic response [2]. CGM is also useful for observing sudden changes in glycaemia after the introduction of dietary interventions and those related to physical activity [3]. Thanks to the accessibility of monitoring systems, the dietary choices of people using technology including combining certain foods, avoiding simple carbohydrates, preparing meals properly, or eating them regularly have gained importance. In addition, CGM is increasingly used in healthy individuals undertaking physical activity. Athletes have the ability to monitor the impact of the type of physical activity combined with diet on their all-day glycaemic profile [4].

Peri-prandial glycaemia

Peri-prandial glycaemia is defined as the change in blood glucose levels depending on the carbohydrate-containing meal consumed [5]. The influence of the peri-prandial glycaemic response is briefly related to the amount and type of food consumed. Optimising the glycaemic profile is important for our health. By doing so, we avoid situations that cause oxidative stress, endothelial dysfunction and increased inflammation, which, in the long term, can contribute to carbohydrate disorders including pre-diabetic conditions [6]. Peri-prandial hyperglycaemia is defined as a large rise in blood glucose levels after eating a meal. It depends on the time, amount, and composition of the meal consumed. A state of peri-prandial hyperglycaemia begins when blood glucose levels rise above the level of 140 mg/dl (7.8 mmol/l) within 1–2 hours after food intake in healthy people without diabetes [7]. In contrast, peri-prandial hypoglycaemia is defined as blood glucose levels below 70 mg/dl (3.9 mmol/l). However, blood glucose levels below 54 mg/dl (3.0 mmol/l) are clinically relevant because blood glucose below this level impairs cognitive function [8]. After eating a meal, especially one containing carbohydrates, blood glucose levels fluctuate. In healthy individuals, the highest peak in blood glucose occurs about one hour after the start of a meal and returns to baseline values within 2–3 hours, and almost every meal peak should be below 140 mg/dl. On the other hand, there should be no situation when the peri-prandial glycaemia is below 70 mg/dl [9]. The best way to observe the fluctuation of glycaemia is using continuous glucose monitoring, even in healthy individuals. Shah et al. in their study observed 153 participants and the influence of their everyday lifestyle on periprandial glycaemia. Overall, 35% of participants spent ≥ 2% of the time with the sensor glucose level < 70 mg/dl (almost 30 min/d), but only 1% of participants spent ≥ 2% of the time at < 54 mg/dl. However, 51% of participants spent ≥ 2% of the time with the sensor glucose level > 140 mg/dl, but < 1% of participants spent ≥ 2% of the time with the level > 180 mg/dl [10].

Purpose and methods

The purpose of this article is to summarise the current knowledge of the effects of various meals on peri-prandial glycaemia in healthy individuals. In addition, an interpretation of factors relevant to the glycaemic profile was undertaken. For the study, the most recent publications posted in the PubMed database from 2016 to 2023 were used, using words such as peri-prandial glycaemia in healthy individuals. Eighty-one publications were analysed, of which 26 relevant articles were used for the paper. This review publication focuses on discussing factors that can reduce the amplitude of peri-prandial glycaemia.

Factors affecting peri-prandial glycaemia

Many factors influence the glycaemic profile, so correct interpretation of data from a continuous glycaemic monitoring system is crucial. These include, i.a.:

• meal: glycaemic index and load, composition, timing, size;
• physical activity: intensity, type, duration, schedule;
• stress;
• metabolic conditions: i.a. insulin resistance, reactive hypoglycaemia [11].

Glycaemic index and glycaemic load of the meal

Our dietary choices have a huge impact on peri-prandial glycaemia. It is very important to choose the right food products, to combine them, and to process them. A properly balanced diet for a low glycaemic index is one of the most important factors for an optimal glycaemic profile. The glycaemic index is defined as the rate at which blood glucose levels rise after eating a particular product. The main disadvantage of the glycaemic index is the lack of information on how elevated and prolonged the glycaemia will be after consuming a carbohydrate-rich food [12]. The glycaemic index is influenced by factors such as the type of carbohydrate contained, the degree of its processing, the type of culinary processing, or the presence of other ingredients such as dietary fibre, protein, fat, or anti-nutrients. In summary, the more processed the product, the faster the carbohydrates it contains are absorbed [13]. On the other hand, a better measure may be the glycaemic load, which additionally takes into account the carbohydrate portion, thus providing a more accurate picture of peri-prandial glycaemia. These conclusions are supported by several studies conducted on a group of healthy individuals. One of them supports the claim that there is a higher glycaemic response after consuming blended fruit than when the fruit is consumed in unprocessed form. Xuejiao Lu et al. in their research containing 19 participants even emphasised how water can influence periprandial glycaemia. The periprandial glycaemia patterns were different depending on the inclusion of water before the meal or not. Without drinking water 30 minutes before there were double small peaks instead of one sharp peak in the second situation [14]. The content of other nutrients in the product, i.a. dietary fibre, is also an important part of the meal. The higher its content, the lower the glycaemic index, resulting in a more stable glycaemic profile. Special attention should be paid to the consumption of products rich in soluble dietary fibre, i.e. pectin and b-glucans, and it is important to increase the intake of resistant starch [15].

Meal composition

Meal composition is one of the most important factors affecting glycaemic response. Combining carbohydrates with protein-containing foods results in lower periprandial glycaemia than eating only carbohydrates in a meal. An example of this phenomenon is a study in which healthy subjects consuming fruit in combination with protein had lower glycaemia than when the meal was fruit alone [16]. The same is true when a fat-containing product is included in the meal instead of protein. There is a huge difference between the glycaemic response to a meal containing only carbohydrates and the glycaemic response to a meal in which carbohydrates are combined with even a small portion of fat [17]. Even when a given meal contains only simple sugars, e.g. in the form of fruit mousse, it is better to consume it with fat, e.g. with nuts. The order in which individual foods are consumed also matters. It has been shown that we should consume protein and fat products first, and carbohydrates last [18].

Meal time

The time at which we eat also affects the glycaemic response. Many publications emphasise that evening meals in healthy individuals exacerbate peri-prandial hyperglycaemia. The supper portion should be smaller and contain a lot of protein and vegetables instead of carbohydrates [19]. There is also a difference between eating the same snack at different times of the day. According to the cited study the highest glycaemic excursions were observed in the morning, while a more dampened but prolonged response was observed in the evening [20].

Meal size

Even the number of meals per day matters for glucose metabolism. Poppy J. and Partners showed improved glucose metabolism in a group of people eating 9 meals a day compared to those eating 3 meals a day. The authors believed that this depended on increased secretion of glucagon-like peptide, which could improve insulin secretion. The observations led to the conclusion that frequent meals have a beneficial effect on glucose metabolism [21].

Physical activity

Regular physical activity is of great importance for glycaemic profile and health status, as well as the prevention of chronic diseases such as metabolic diseases, cancer, and depression. A sedentary lifestyle impairs abnormal carbohydrate metabolism and causes a higher glycaemic peak after eating an improperly balanced meal [22]. Numerous studies show that an 8-week exercise program is sufficient to improve health, reduce body weight, and lower glucose levels. Data from a continuous glucose monitoring system have been used to track blood glucose [23]. Publications in recent years have emphasised that even the introduction of occasional physical activity can have a beneficial effect on glucose metabolism, as well as glucose uptake by skeletal muscle. The example can be in the research of Dempsey et al. in which 24 inactive obese participants started light exercise. After finishing the observation, postprandial glycaemia changed resulting lower of 39% mean change [24]. It is important to emphasise that the effects on insulin sensitivity persist even several hours after exercise. Regular physical activity is the key to improving glycaemic response and avoiding glycaemic variability. Even when we lead sedentary lifestyles, undertaking physical activities such as brisk walking or other simple activities have a beneficial effect on our glucose metabolism [25]. The timing of exercise is as important as its duration. Studies suggest that starting light activity immediately after eating can lower periprandial blood glucose levels. Even 10 minutes of low-intensity activity or a type of exercise can help treat high blood glucose levels [26].

Stress and metabolic conditions

Stressful conditions also affect glycaemic metabolism independently of food intake and exercise. Stress hormones such as epinephrine and cortisol increase the risk of diabetes, insulin resistance, dyslipidaemia, and hypertension [27]. The correct interpretation of data from continuous glycaemic monitoring should additionally take into account the stressful situation the person is experiencing. Correct interpretation of glycaemia from a CGM sensor requires knowledge of the contribution of numerous factors that affect peripheral glycaemia. Even our gut microbiome modulates insulin secretion. The study by Kreznar et al. emphasises that we have metabolic strains in response to a high-fat/high-sucrose diet. Confirmation of the importance of our nutritional choice on our microbiome was shown in another study in which a high-fat diet can promote metabolic syndrome [28].

Summary

In summary, peri-prandial glycaemia is influenced by several factors related to the proper choice of food products and their preparation. Among the most important of these are the amount of macronutrients in the diet, mainly carbohydrates, the combination of carbohydrates with protein or fat in a single meal, or the dietary fibre content of a given product. The culinary processing of the food in question and, in some cases, the degree of maturity of the food is also important. It is important to consider that periprandial glycaemia is influenced not only by the meal but also by the type of physical activity and the body’s response to stress. Nowadays, continuous glycaemic monitoring systems are increasingly used to assess peri-prandial glycaemia in healthy individuals. In particular, they are used by people who undertake physical activity, i.e. athletes, who adjust training and diet on the basis of observation of the glycaemic profile. It should also be noted that healthy individuals after eating an improperly composed meal and leading a sedentary lifestyle have a worse glycaemic response, leading to the development of overweight, obesity, diabetes, and cardiovascular disease.

References