The review aims to explore the potential benefit and risk of high-protein diets (HPD) regarding the comorbidity of sarcopoenia and CVD in the setting of cardiac rehabilitation (CR). CR is standard care for individuals who have experienced a cardiac event, but the current practice of predominantly aerobic exercise, a lower-fat diet and weight loss poorly addresses the issue of sarcopoenia. HPD, especially when combined with resistance exercise (RE), may be valuable adjuncts to current CR practice and benefit both muscle and cardiovascular health. Meta-analyses and randomised controlled trials of HPD and CVD risk show beneficial but variable effects regarding weight loss, the lipid profile, insulin resistance and lean body mass in those living with or high risk of CVD. Meta-analyses of prospective cohort studies on hard CVD endpoints favour lower- and plant-protein diets over higher animal protein, but the evidence is inconsistent. HPD augment the strength and muscle gaining benefits of RE in older populations, but there are no published data in those living with CVD providing promising opportunities for CR research. HPD raise concern regarding renal and bone health, the microbiome, branched chain amino acids and environmental sustainability and findings suggest that plant-based HPD may confer ecological and overall health advantages compared to animal-based HPD. However, incorporating RE with HPD might alleviate certain health risks. In conclusion, a largely plant-based HPD is deemed favourable for CR when combined with RE, but further research regarding efficacy and safety in CR populations is needed.

The aim of the present study was to evaluate the impact of a high-protein meal replacement (HPMR) on weight and metabolic, lipid and inflammatory parameters in overweight/obese Asian Indians. In this 12-week open-label, parallel-arm randomised controlled trial, 122 overweight/obese men and women were administered either a HPMR or a control diet after 2 weeks of diet and exercise run-in. Body weight, waist circumference (WC), percentage body fat (%BF), fasting blood glucose, post-oral glucose tolerance test (post-OGTT) blood glucose, fasting and post-OGTT serum insulin, lipid profile, high-sensitivity C-reactive protein (hs-CRP), kidney function and hepatic aminotransferases were assessed before and after the intervention. Additional improvement in mean values for the following parameters in the HPMR group compared with the control group was observed: body weight, 4·9 % (95 % CI 3·8, 6·1; P<0·001); WC, 3·8 % (95 % CI 2·5, 5·1; P<0·001); %BF, 6·3 % (95 % CI 4·3, 8·2; P<0·001); systolic blood pressure, 2·8 % (95 % CI 0·4, 5·1; P=0·002); diastolic blood pressure, 3·5 % (95 % CI 0·7, 6·3; P= 0·01); post-OGTT blood glucose, 7·3 % (95 % CI 1·4, 13·1; P=0·02); total cholesterol, 2·5 % (95 % CI 1·6, 3·5; P<0·001); LDL-cholesterol, 7·3 % (95 % CI 1·7, 12·9; P<0·01); alanine aminotransferase, 22·0 % (95 % CI 2·1, 42; P=0·03) and aspartate aminotransferase, 15·2 % (95 % CI 0·9, 29·5; P=0·04). The absolute reduction in BMI was 0·9 units in the intervention arm compared with the control arm (–0·9 %, 95 % CI –1·4, –0·5; P<0·001) and in serum TAG was 11·9 mg/dl (–11·9 mg/dl, 95 % CI –21·1, –2·7; P<0·01). The reduction in fasting serum insulin in the intervention v. the control arm was 3·8 v. 0 % (P=0·002); post-OGTT serum insulin was 50·3 v. 77·3 mU/l (P=0·005); and hs-CRP, 16·7 % v. 0 % (P=0·002). These findings show that intervention with HPMR may lead to significant weight loss and improvement in obesity measures, metabolic, lipid and inflammatory parameters and hepatic transaminases in overweight/obese Asian Indians.

High-protein diets are an effective means for weight loss (WL), but the mechanisms are unclear. One hypothesis relates to the release of gut hormones by either protein or amino acids (AA). The present study involved overweight and obese male volunteers (n 18, mean BMI 36·8 kg/m2) who consumed a maintenance diet for 7 d followed by fully randomised 10 d treatments with three iso-energetic WL diets, i.e. with either normal protein (NP, 15 % of energy) or high protein (HP, 30 %) or with a combination of protein and free AA, each 15 % of energy (NPAA). Psychometric ratings of appetite were recorded hourly. On day 10, plasma samples were taken at 30 min intervals over two consecutive 5 h periods (covering post-breakfast and post-lunch) and analysed for AA, glucose and hormones (insulin, total glucose-dependent insulinotropic peptide, active ghrelin and total peptide YY (PYY)) plus leucine kinetics (first 5 h only). Composite hunger was 16 % lower for the HP diet than for the NP diet (P< 0·01) in the 5 h period after both meals. Plasma essential AA concentrations were greatest within 60 min of each meal for the NPAA diet, but remained elevated for 3–5 h after the HP diet. The three WL diets showed no difference for either fasting concentrations or the postprandial net incremental AUC (net AUCi) for insulin, ghrelin or PYY. No strong correlations were observed between composite hunger scores and net AUCi for either AA or gut peptides. Regulation of hunger may involve subtle interactions, and a range of signals may need to be integrated to produce the overall response.

High-protein (HP) diets are effective anti-steatotic treatment options for patients with non-alcoholic fatty liver disease, but whether these diets also decrease steatosis in hyperlipidaemic conditions is not known. The aim of the present study was to determine the effects of a HP diet on hepatic steatosis and inflammation in hyperlipidaemic mice. Hyperlipidaemic male and female APOE2 knock-in (APOE2ki) mice were fed a semi-synthetic low-protein (LP) or HP diet in combination with a low-fat diet or a high-fat diet for 3 weeks. The HP diets reduced hepatic fat and cholesterol concentrations to 40–55 % of those induced by the corresponding LP diets and attenuated hepatic inflammation mildly. The VLDL-associated plasma cholesterol concentrations decreased to 60–80 %, but those of TAG increased 3–4-fold. APOE2-mediated restriction of fat import into the liver did not modify the effects of a HP diet previously observed in wild-type mice. Female APOE2ki mice exhibited a higher expression of lipogenic, cholesterol-synthesising, inflammatory and cell-stress genes than wild-type female or male APOE2ki mice, but a similar response to HP diets. Low Apob expression and unchanged plasma APOB100 concentrations suggest that HP diets increase the plasma concentrations of TAG by slowing their clearance. The decrease in plasma leptin and hepatic fat and glycogen concentrations and the increase in fatty acid-oxidising gene and phosphoenolpyruvate carboxykinase 1 protein expression suggest a HP diet-mediated increase in mitochondrial metabolism. In conclusion, a HP diet reduces hepatic lipid content in dyslipidaemic mice and lowers the activation status of inflammatory cells in the liver.

High-protein diets are popular for weight management, but the health effects of such diets in diabetic persons are inconclusive. The aim of the present meta-analysis was to examine the effects of high-protein diets on body weight and metabolic risk factors in patients with type 2 diabetes. We searched the PubMed and Cochrane Library databases for relevant randomised trials up to August 2012. Either a fixed- or a random-effects model was used to combine the net changes in each outcome from baseline to the end of the intervention. Overall, nine trials including a total of 418 diabetic patients met our inclusion criteria. The study duration ranged from 4 to 24 weeks. The actual intake of dietary protein ranged from 25 to 32 % of total energy in the intervention groups and from 15 to 20 % in the control groups. Compared with the control diets, high-protein diets resulted in more weight loss (pooled mean difference: − 2·08, 95 % CI − 3·25, − 0·90 kg). High-protein diets significantly decreased glycated Hb A1C (HbA1C) levels by 0·52 (95 % CI − 0·90, − 0·14) %, but did not affect the fasting blood glucose levels. There were no differences in lipid profiles. The pooled net changes in systolic and diastolic blood pressure were − 3·13 (95 % CI − 6·58, 0·32) mmHg and − 1·86 (95 % CI − 4·26, 0·56) mmHg, respectively. However, two studies reported a large influence on weight loss and HbA1C levels, respectively. In summary, high-protein diets (within 6 months) may have some beneficial effects on weight loss, HbA1C levels and blood pressure in patients with type 2 diabetes. However, further investigations are still required to draw a conclusion.

Overweight and obesity are growing problems both in Canada and around the world. Obesity is associated with a number of chronic diseases including type 2 diabetes and CVD, which puts a tremendous burden on the health care systems in place. The present study sought to investigate whether there were differences in the effectiveness of three low-fat, hypo- and isoenergetic diets differing in protein:carbohydrate ratio, low protein (LP, 1 g protein:4 g carbohydrate), normal protein (NP, 1 g protein:2 g carbohydrate) or high protein (HP, 1 g protein:1 g carbohydrate), on weight loss and markers of the metabolic syndrome (MetS) in overweight women. Subjects were randomly assigned to receive one of three intervention diets, all of which included a 60 min exercise programme three times/week for 12 weeks. Of the total subjects, fifty-four overweight and obese local women with MetS risk factors completed the study. All groups had similar improvements in body weight, insulin sensitivity, lipid profile, blood pressure and fitness. Subjects reported that the NP diet was easier to comply with and achieved better improvements in body fat, waist circumference and waist:hip ratio, and preservation of lean mass compared with the other two diets. In conclusion, energy restriction and exercise both facilitate weight loss in overweight and obese subjects and reduce symptoms of the MetS. A diet with a 1:2 protein:carbohydrate ratio promoted better improvements than either the LP or HP diets, and may be superior in reducing long-term chronic disease risk in this population.

There are concerns that weight-loss (WL) diets based on very low carbohydrate (LC) intake have a negative impact on antioxidant status and biomarkers of cardiovascular and metabolic health. Obese men (n 16) participated in a randomised, cross-over design diet trial, with food provided daily, at approximately 8·3 MJ/d (approximately 70 % of energy maintenance requirements). They were provided with two high-protein diets (30 % of energy), each for a 4-week period, involving a LC (4 % carbohydrate) and a moderate carbohydrate (MC, 35 % carbohydrate) content. Body weight was measured daily, and weekly blood samples were collected. On average, subjects lost 6·75 and 4·32 kg of weight on the LC and MC diets, respectively (P < 0·001, sed 0·350). Although the LC and MC diets were associated with a small reduction in plasma concentrations of retinol, vitamin E (α-tocopherol) and β-cryptoxanthin (P < 0·005), these were still above the values indicative of deficiency. Interestingly, plasma vitamin C concentrations increased on consumption of the LC diet (P < 0·05). Plasma markers of insulin resistance (P < 0·001), lipaemia and inflammation (P < 0·05, TNF-α and IL-10) improved similarly on both diets. There was no change in other cardiovascular markers with WL. The present data suggest that a LC WL diet does not impair plasma indices of cardiometabolic health, at least within 4 weeks, in otherwise healthy obese subjects. In general, improvements in metabolic health associated with WL were similar between the LC and MC diets. Antioxidant supplements may be warranted if LC WL diets are consumed for a prolonged period.

Consumption of high-protein (HP) diets is postulated to exert a negative influence on bone and renal health. However, no conclusive evidence has been presented related to this issue or to the potential protective action of resistance training on HP-induced systemic effects. We examined the effects of HP diet consumption on food intake, body-weight gain, body composition, and renal, bone and metabolic parameters of rats performing resistance training. A total of ninety-six adult male Wistar rats were randomly distributed in twelve experimental groups (n 8): normal-protein (10 %) or HP (45 %) diets, with or without resistance training, killed for experimental periods of 1, 2 or 3 months. Diets were based on a commercial whey protein hydrolysate. Consumption of HP diets and resistance training significantly affected food intake, body weight and body composition, as well as the plasma levels of total cholesterol, HDL-cholesterol and TAG. The buffering action of resistance training on such diet-induced alterations was especially evident in the levels of plasma TAG. Consumption of HP diets led to a considerable increase in kidney weight, urinary volume and acidity, as well as in the urinary excretion of Ca, with a parallel reduction in the urinary excretion of citrate (P < 0·05). No apparent deleterious effect on bone mineral content was found. In conclusion, consumption of HP diets caused alterations in renal health status and some metabolic parameters, but did not seem to affect bone status. Resistance training had a protective action against alterations of renal health status and some metabolic parameters such as plasma TAG.

Two types of relatively high-protein diets, with a normal or low proportion of carbohydrates, have been shown effective for weight loss. The objective was to assess the significance of the presence or absence of carbohydrates and the proportion of fat in high-protein diets for affecting appetite suppression, energy expenditure, and fat oxidation in normal-weight subjects in energy balance. Subjects (aged 23 (sd 3) years and BMI 22·0 (sd 1·9) kg/m2) were stratified in two groups. Each was offered two diets in a randomised cross-over design: group 1 (n 22) – normal protein (NP; 10, 60 and 30 % energy (En%) from protein, carbohydrate and fat), high protein (HP; 30, 40 and 30 En%); group 2 (n 23) – normal protein (NP-g; 10, 60 and 30 En%), high protein, carbohydrate-free (HP-0C; 30, 0 and 70 En%) for 2 d; NP-g and HP-0C were preceded by glycogen-lowering exercise (day 1). Appetite was measured throughout day 2 using visual analogue scales (VAS). Energy expenditure (EE) and substrate oxidation (respiratory quotient; RQ) were measured in a respiration chamber (08.00 hours on day 2 until 07.30 hours on day 3). Fasting plasma β-hydroxybutyrate (BHB) concentration was measured (day 3). NP-g and NP did not differ in hunger, EE, RQ and BHB. HP-0C and HP v. NP-g and NP, respectively, were lower in hunger (P < 0·05; P < 0·001) and RQ (P < 0·01; P < 0·001) and higher in EE (P < 0·05; P = 0·07) and BHB (P < 0·05; P < 0·001). Hunger and RQ were lower with HP-0C than HP (693 (sd 208) v. 905 (sd 209) mm VAS × 24 h, P < 0·01; 0·76 (sd 0·01) v. 0·81 (sd 0·02), P < 0·01); BHB was higher (1349 (sd 653) v. 332 (sd 102) μmol/l; P < 0·001). ΔHunger, ΔRQ, and ΔBHB were larger between HP-0C–NP-g than between HP–NP ( − 346 (sd 84) v. − 107 (sd 52) mm VAS ×  24 h, P < 0·01; − 0·09 (sd 0·00) v. − 0·05 (sd 0·00), P < 0·001; 1115 (sd 627) v. 104 (sd 42) μmol/l, P < 0·001). In conclusion, appetite suppression and fat oxidation were higher on a high-protein diet without than with carbohydrates exchanged for fat. Energy expenditure was not affected by the carbohydrate content of a high-protein diet.