**3. Metabolic benefits of meal replacement**

Portion size is a key factor in determining energy intake and may be closely linked to obesity. Research indicates that portion size is directly correlated with energy intake, suggesting that controlling portion size is an effective approach to reduce energy intake and combat obesity [22]. Among the few portion control tools researched to date, liquid MR are considered among the most effective and consistent, particularly if combined with other efforts to encourage consumption of high‐nutrient‐dense, low‐energy‐dense foods [22]. Furthermore, MR promote adherence to a restricted calorie diet due to simple preparation and convenience compared to preparing and cooking low‐calorie foods at home. MR generally contain a tight range of total calories, macro‐ and micronutrients (**Figure 3**), and are a nutrient‐dense tool, especially useful for supporting adherence to a calorie‐restricted diet through portion control. Satiety and appetite are known to impact total energy intake, as well as food choices and eating behavior. Both are regulated by a combination of mechanical and endocrine effects ranging from the gut to the brain. With respect to diet, protein has been identified as an important contributor to satiety, defined as the absence of hunger between meals. Dietary protein can induce satiety through several mechanisms including thermic effects and induction of gut hormones such as cholecystokinin (CCK) and glucagon‐like peptide 1 (GLP‐1) and ghrelin [23]. Intervention studies show that increased protein intake, using protein‐enriched MR, is effective at increasing satiety, reducing hunger sensations, decreasing energy intake

**Figure 2.** Weight loss and maintenance from randomized controlled trials ≥1 year in duration involving meal replacement.

Many authoritative bodies around the world have sanctioned the use of MR for weight loss and control. As far back as the mid‐1980s, Codex Alimentarius recognized the use of MRs for

and facilitating weight loss in obese subjects [24, 25].

260 Superfood and Functional Food - An Overview of Their Processing and Utilization

Weight loss in obese subjects during an intervention is comprised of water, fat and lean (muscle) mass. The amount and extent of fat and muscle loss depend on the specific weight loss intervention. As lean mass determines the basal metabolic rate (BMR), the goal for any weight loss program is to lose fat mass, while preserving muscle mass. This helps to maintain a higher BMR, which in turn helps to maintain energy expenditure, which can often decline with weight loss. Use of protein‐enriched MR products has been shown to effectively maintain lean body mass during weight loss [24, 29], particularly when combined with resistance exercise [30].

Glycemic index (GI) represents a measure of the ability or rapidity of a given food to raise an individual's postprandial blood glucose level. GI is determined for a given food in reference to a standard food, usually white bread, and reflects the blood glucose‐raising ability of digestible carbohydrates in a given food [31]. Examples of relative GI values of different foods can be found in **Table 2**.

A growing body of evidence suggests that the GI and glycemic load (GL, a measure of how much a given food will raise an individual's blood glucose level following consumption) of the diet play an important role in human metabolic functions and health. High GI foods and a high GL stimulate a rapid rise in insulin levels, which on a chronic basis can result in insulin resistance [32, 33]. The GL of a food is calculated by multiplying its GI by the amount of carbohydrate it contains per serving, and then dividing by 100. GL is a function of the amount of carbohydrate intake and the GI of the food. In contrast, GI is an inherent property of a food, independent of the amount of carbohydrate ingested. The GI value of a diet can impact insulin sensitivity and glucose metabolism [34]. Blood sugar levels have also been implicated in appetite control, suggesting that. Furthermore, MR promote adherence to a restricted calorie diet due to simple preparation and convenience compared to preparing and cooking low‐calorie foods at home. The GI of a diet may impact overall food and energy intake [35]. Accordingly, low‐GI diets have been shown to be an effective approach for managing diabetes [36, 37] and obesity [38, 39]. The combination of a high‐protein, low‐GI diet in obese subjects is effective at inducing weight loss and maintenance of lean body mass [25, 36, 40]. Although it varies by formulation, MR tend to be high in protein and have a low GI (<55), making them ideal for incorporation into an overall low‐GI diet plan.


**Table 2.** Glycemic index (GI) values of select foods.

As with insulin sensitivity, the degree of intrabdominal and visceral fat is tightly linked to metabolic syndrome. Surrounding the body's critical organs, such as the heart and liver, visceral fat stimulates systemic inflammation and is known as an increasingly serious risk factor for chronic diseases, including cardiovascular disease and diabetes [41]. In simple terms, "sarcopenic obesity" can be defined as low skeletal muscle mass and strength combined with excess body fat, much of which is visceral fat [42, 43]. The concept has also been described as "thin outside, fat inside" or "TOFI" [44]. Related to obesity, individuals can have the same body mass index (BMI), but vastly different inflammatory states and risk levels due to differences in distribution and degree of visceral fat [45]. As there is as yet no medical cure, resistance and strength exercise, combined with a high‐protein diet, is recommended as one of the only effective means of addressing sarcopenic obesity and complications of excess visceral fat [30, 46]. When used in conjunction with reduced total calorie intake and resistance exercise, MR can also be effective at reducing visceral fat [19, 30, 47].

With respect to safety, use of MR for weight control and other metabolic benefits is among the safest approaches studied. Many individual intervention studies [48–50] as well as systematic reviews [51] have confirmed that MR safely facilitate weight loss and maintenance.
