Protein is absorbed across the entire intestinal tract, but is primarily absorbed in the mid-ileum, which is bypassed in many bariatric procedures. After bowel bypass only 57 % of ingested protein is estimated to be absorbed [8]. Research has shown that protein malabsorption occurs in 7–21 % after biliopancreatic diversion (BPD)/roux en Y gastric bypass (RYGB) and this is accompanied by a large loss of fat free mass [8–10]. Interestingly protein malabsorption can also occur after laparoscopic adjustable gastric banding (LAGB), vertical banded gastroplasty (VBG) and laparoscopic sleeve gastrectomy (LSG) [11–13]. Thus not just malabsorption but many other factors may also be involved in protein calorie malnutrition in bariatric patients including lack of adequate intake, food intolerance, food aversions, socio-economic status, vomiting, and diarrhea [14]. Therefore, most bariatric patients irrespective of the type of bariatric procedure will be at a risk of protein malnutrition.

It has been shown that post bariatric patients with inadequate protein intake find it difficult to lose weight and maintain weight [2]. Loss of lean body mass is more than expected with a consequent reduction in basal metabolic rate and physiological damage. Conversely, a protein-rich diet can lead to increased satiety, enhance weight loss and improved body composition. Hence increased consumption of dietary protein improves body weight management and prevention of weight regain in post bariatric surgery patients [2].

Motivating protein consumption post surgery is really difficult as protein-rich foods are difficult to chew and swallow, inducing aversion more easily than foods rich in carbohydrates, and even tend to reduce appetite [15, 16]. Dry or tough pork, poultry and red meat are protein sources that tend to be more difficult to tolerate but the tolerance of protein-rich foods tends to improve at 1 year after bariatric surgery [17].

It has been shown that the addition of 0.5 g protein/kg ideal weight increased the serum albumin levels by 0.11 g/dl indicating that the visceral protein status of bariatric surgery patients can be easily improved by consuming an adequate protein diet [19]. In a study on complicated post–bariatric surgery patients requiring artificial nutritional support, high protein low calorie feedings resulted in positive nitrogen balance, better wound healing along with weight loss [20].

A prospective study on daily protein intake of >1 g/kg/day resulted in increased weight loss, decreased percentage of body fat and improved percentage of lean mass 1 year after laparoscopic RYGB [18]. For bariatric surgery patients, the recommended daily protein consumption is 1.5 g/kg ideal weight which is about 60–120 g of protein daily to maintain adequate FFM during weight loss [21]. However a higher protein intake of 1.5–2.0 g of protein/kg ideal body weight per day is encouraged after malabsorptive procedures like BPD/DS patients. For Indian patients, a protein intake of 1–1.5 g/kg ideal body weight for restricted procedures and 1.5–2 g/kg ideal body weight for malabsorptive procedure such as the duodenal switch, BPD and long limb RYGB is recommended [22].

An important point to note is that a protein-rich diet usually includes at least 25–30 % of proteins expressed as percentage of energy from protein for a normal calorie diet. However for a low calorie diet this percentage of energy from protein may not meet the requirements in absolute terms (i.e., grams of protein) and the proportion of proteins need to be increased [23]. For example, a 2866 kcal/day diet can achieve a protein intake of 67–100 g (10–15 % protein), whereas for a 478-kcal/day very-low-calorie diet 47 % of calories should come from protein to obtain 52 g protein.

It is also to be noted that a balanced intake of protein is important. It was shown that 30 g of protein every meal helps maintain healthy bones and muscles. It is also suggested that patients should consume a high protein intake for breakfast to relieve the catabolic state of overnight fasting and that protein rich foods should be consumed before carbohydrate and fat foods [24]. Several other authors also have supported the intake of a generous and balanced protein at each meal (>30 g) for optimal protein synthesis in the muscle [25, 26]. Also consumption of high protein meals throughout the day prolongs satiety compared with consuming standard-protein meals. A randomized cross over study showed a protein rich breakfast might be a useful strategy to improve satiety in overweight or obese teenage girls [27]. Consumption of a moderate amount of protein at each meal stimulated 24 h muscle protein synthesis more effectively than taking protein in an evening meal [28].

The quality of protein each meal also needs to be considered. Protein quality is measured by its essential amino acid (EAA) content, unique amino acid profile, and the digestibility of each essential amino acid in the protein [29]. Animal origin foods such as meat, fish, eggs, poultry and dairy products are rich sources of protein but are also high in fat. Lean meat, egg white, skimmed milk and nonfat cheese are rich sources of protein but are low in fat. Plant foods like legumes, nuts, soy and grains are also rich in protein. Protein supplements have high protein with low carbohydrate and fat content. However it has been demonstrated that plant based proteins such as soy and wheat resulted in lower muscle protein synthesis than animal based proteins [30]. This could be due to lower anabolic properties of plant proteins and lack of specific essential amino acids such as leucine, arginine and citruline [31].

Several studies have underscored the importance of leucine-rich diet [32]. Many studies have suggested that high protein diets are beneficial partly due to branched chain amino acids especially leucine, which favors the maintenance of muscle mass. It has been shown that during catabolic periods particularly in a post bariatric situation, muscle protein synthesis is stimulated by leucine supplementation. Also, leucine plays a role in the insulin signaling pathway which maintains protein synthesis [32]. The richest source of leucine is whey protein (14 %) followed by casein (10.1 %), egg protein (8.5 %), isolated soy proteins (8 %) and wheat protein (7 %). A protein rich and leucine rich diet promotes long term weightloss and improved body composition It has been estimated that stimulation of muscle protein synthesis would be optimized with 18 g Indispensible Amino Acids (IAA) or Essential Amino Acids (EAA), including 2.5 g leucine, at each of the three meals per day [33].