High-protein Weight-loss Diets Research Articles

Dietary Milk or Isolated Legume Proteins Modulate Intestinal Microbiota Composition in Rats.

Shifts toward increased proteolytic fermentation, such as, for example, in athlete and high-protein weight loss diets, may alter the relative abundance of microbial species in the gut and generate bioactive, potentially deleterious metabolic products. In the current investigation, intestinal (caecal) microbiota composition was studied in rats fed diets differing only in their constituent proteins: milk (casein (CAS), lactalbumin (LA)) or legume (Cicer arietinum, Lupinus angustifolius) protein isolates (chickpea protein isolate (CPI), lupin protein isolate (LI)). ANOSIM and Discriminant Analysis showed significant (p < 0.05) differences at both family and genus levels in both microbiota composition and functionality as a consequence of feeding the different proteins. Differences were also significant (p < 0.05) for predicted functionality parameters as determined by PICRUSt analysis. LA induced a generally healthier microbiota composition than CAS, and higher amounts of Methanobrevibacter spp. and Methanogenic_PWY were found in the LI group. LEfSe analysis of bacterial composition and functional activities revealed a number of groups/functions able to explain the different effects found with milk and legume protein isolates. In conclusion, the mostly beneficial modulation of intestinal microbiota generally found with legume-based diets is likely to be due, at least in part, to their constituent proteins.

Effects of Dietary Protein Source and Quantity on Bone Morphology and Body Composition Following a High-Protein Weight-Loss Diet in a Rat Model for Postmenopausal Obesity.

Higher protein (>30% of total energy, HP)-energy restriction (HP-ER) diets are an effective means to improve body composition and metabolic health. However, weight loss (WL) is associated with bone loss, and the impact of HP-ER diets on bone is mixed and controversial. Recent evidence suggests conflicting outcomes may stem from differences in age, hormonal status, and the predominant source of dietary protein consumed. Therefore, this study investigated the effect of four 12-week energy restriction (ER) diets varying in predominate protein source (beef, milk, soy, casein) and protein quantity (normal protein, NP 15% vs. high, 35%) on bone and body composition outcomes in 32-week-old obese, ovariectomized female rats. Overall, ER decreased body weight, bone quantity (aBMD, aBMC), bone microarchitecture, and body composition parameters. WL was greater with the NP vs. HP-beef and HP-soy diets, and muscle area decreased only with the NP diet. The HP-beef diet exacerbated WL-induced bone loss (increased trabecular separation and endocortical bone formation rates, lower bone retention and trabecular BMC, and more rod-like trabeculae) compared to the HP-soy diet. The HP-milk diet did not augment WL-induced bone loss. Results suggest that specific protein source recommendations may be needed to attenuate the adverse alterations in bone quality following an HP-ER diet in a model of postmenopausal obesity.

Sapogenol is a Major Microbial Metabolite in Human Plasma Associated with High Protein Soy-Based Diets: The Relevance for Functional Food Formulations.

Legumes are a source of health-promoting macro- and micronutrients, but also contain numerous phytochemicals with useful biological activities, an example of which are saponins. Epidemiological studies suggest that saponins may play a role in protection from cancer and benefit human health by lowering cholesterol. Therefore, they could represent good candidates for specialised functional foods. Following the consumption of a soya-rich high-protein weight-loss diet (SOYA HP WL), the concentrations of Soyasaponin I (SSI) and soyasapogenol B (SSB) were determined in faecal samples from human volunteers (n = 10) and found to be between 1.4 and 17.5 mg per 100 g fresh faecal sample. SSB was the major metabolite identified in volunteers’ plasma (n = 10) after consumption of the soya test meal (SOYA MEAL); the postprandial (3 h after meal) plasma concentration for SSB varied between 48.5 ng/mL to 103.2 ng/mL. The metabolism of SSI by the gut microbiota (in vitro) was also confirmed. This study shows that the main systemic metabolites of soyasaponin are absorbed from the gut and that they are bioavailable in plasma predominantly as conjugates of sapogenol. The metabolism and bioavailability of biologically active molecules represent key information necessary for the efficient development of functional foods.

Dietary Protein Modifies the Effect of the MC4R Genotype on 2-Year Changes in Appetite and Food Craving: The POUNDS Lost Trial.

Background: The melanocortin-4 receptor (MC4R) plays a pivotal role in the regulation of appetite and eating behavior. Variants in the MC4R gene have been related to appetite and obesity.Objective: We aimed to examine whether weight-loss diets modified the effect of the "obesity-predisposing" MC4R genotype on appetite-related measures in a randomized controlled trial.Methods: A total of 811 overweight and obese subjects [25 ≤ body mass index (BMI; kg/m2) ≤ 40] aged 30-70 y were included in the 2-y POUNDS Lost (Preventing Overweight Using Novel Dietary Strategies) trial. We genotyped MC4R rs7227255 in 735 overweight adults and assessed appetite-related characteristics, including craving, fullness, hunger, and prospective consumption, as well as a composite appetite score. We examined the effects of the genotype-by-weight-loss diet intervention interaction on appetite variables by using general linear models in both the whole population and in white participants only.Results: We found that dietary protein intake (low compared with high: 15% of energy compared with 25% of energy, respectively) significantly modified MC4R genetic effects on changes in appetite score and craving (P-interaction = 0.03 and 0.02, respectively) at 2 y, after adjustment for age, sex, ethnicity, baseline BMI, weight change, and baseline perspective phenotype. The obesity-predisposing A allele was associated with a greater increase in overall appetite score (β = 0.10, P = 0.05) and craving (β = 0.13, P = 0.008) compared with the non-A allele among participants who consumed a high-protein diet. MC4R genotype did not modify the effects of fat or carbohydrate intakes on appetite measures. Similar interaction patterns were observed in whites.Conclusion: Our data suggest that individuals with the MC4R rs7227255 A allele rather than the non-A allele might experience greater increases in appetite and food craving when consuming a high-protein weight-loss diet. This trial was registered at clinicaltrials.gov as NCT00072995.

Long-Term Effects of a Randomised Controlled Trial Comparing High Protein or High Carbohydrate Weight Loss Diets on Testosterone, SHBG, Erectile and Urinary Function in Overweight and Obese Men.

IntroductionObesity is associated with reduced testosterone and worsened erectile and sexual function in men. Weight loss improves these outcomes. High protein diets potentially offer anthropometric and metabolic benefits, but their effects on reproductive and sexual outcomes is not known.AimTo examine the long-term effects of weight loss with a higher protein or carbohydrate diet on testosterone, sex hormone binding globulin, erectile dysfunction, lower urinary tract symptoms and sexual desire in overweight and obese men.MethodsOne-hundred and eighteen overweight or obese men (body mass index 27–40 kg/m2, age 20–65 years) were randomly assigned to an energy restricted higher protein low fat (35% protein, 40% carbohydrate, 25% fat; n = 57) or higher carbohydrate low fat diet (17% protein, 58% carbohydrate, 25% fat, n = 61) diet for 52 weeks (12 weeks weight loss, 40 weeks weight maintenance). Primary outcomes were serum total testosterone, sex hormone binding globulin and calculated free testosterone. Secondary outcomes were erectile function as assessed by the International Index of Erectile Function (IIEF) (total score and erectile function domain), lower urinary tract symptoms and sexual desire.ResultsTotal testosterone, sex hormone binding globulin and free testosterone increased (P<0.001) and the total IIEF increased (P = 0.017) with no differences between diets (P≥0.244). Increases in testosterone (P = 0.037) and sex hormone binding globulin (P<0.001) and improvements in the total IIEF (P = 0.041) occurred from weeks 0–12 with a further increase in testosterone from week 12–52 (P = 0.002). Increases in free testosterone occurred from week 12–52 (p = 0.002). The IIEF erectile functon domain, lower urinary tract symptoms and sexual desire did not change in either group (P≥0.126).ConclusionsIn overweight and obese men, weight loss with both high protein and carbohydrate diets improve testosterone, sex hormone binding globulin and overall sexual function.Trial RegistrationAnzctr.org.au ACTRN12606000002583

Su1874 High and Standard Protein Weight Loss Diets Modulate Colonic Fermentation but Do Not Affect Fecal Water Toxicity

Su1874 High and Standard Protein Weight Loss Diets Modulate Colonic Fermentation but Do Not Affect Fecal Water Toxicity

Appetite control and biomarkers of satiety with vegetarian (soy) and meat-based high-protein diets for weight loss in obese men: a randomized crossover trial

There is limited evidence with regard to the effect of different sources of protein on appetite during weight loss. Vegetarian and meat-based high-protein diets may have contrasting effects on appetite and biomarkers of protein-induced satiety. The aim was to assess appetite response to meat or vegetarian high-protein weight-loss (HPWL) diets in obese men to monitor plasma amino acid profile and gut peptide response as potential satiety biomarkers. Twenty obese [body mass index (in kg/m²): 34.8] men participated in a dietary intervention study. After 3 d of a maintenance diet, they were provided in a crossover design with either a vegetarian HPWL (Soy-HPWL) or a meat-based HPWL (Meat-HPWL) diet for 2 wk. Both diets comprised 30% protein, 30% fat, and 40% carbohydrate, provided to measured resting metabolic rate. Body weight and the motivation to eat were measured daily. Plasma satiety biomarkers were collected during a test-meal challenge (5 h) at the end of each diet period. Over the 2 wk, subjects lost, on average, 2.41 and 2.27 kg with consumption of the Soy- and Meat-HPWL diets, respectively [P = 0.352; SE of the difference (SED): 0.1]. ANOVA confirmed that subjectively rated hunger (P = 0.569; SED: 3.8), fullness (P = 0.404; SED: 4.1), desire to eat (P = 0.356; SED: 3.7), preservation of lean body mass (P = 0.334; SED: 0.2), and loss of percentage fat mass (P = 0.179; SED: 0.2) did not differ between the 2 HPWL diets. There were differences in absolute concentrations of ghrelin and peptide YY between the 2 HPWL diets, although the response as net area under the curve was not different. Appetite control and weight loss were similar for both HPWL diets. Gut hormone profile was similar between the diets, which suggests that vegetarian diets can be as effective as meat-based diets for appetite control during weight loss.

High protein weight loss diets in obese subjects with type 2 diabetes mellitus

Background and aimDiets where carbohydrate has been partially exchanged for protein have shown beneficial changes in persons with type 2 diabetes but no studies have enrolled people with albuminuria. We aim to determine if a high protein to carbohydrate ratio (HPD) in an energy reduced diet has a beneficial effect on metabolic control and cardiovascular risk factors without negatively affecting renal function. Method and resultsAdult, overweight participants with type 2 diabetes, with albuminuria (30–600 mg/24 h or an albumin-to-creatinine ratio of 3.0–60 mg/mmol), and estimated GFR of >40 ml/min/1.73 m2 were enrolled. Participants were randomized to an HPD or an SPD. Protein:fat:carbohydrate ratio was 30:30:40% of energy for the HPD and 20:30:50% for the SPD. Main outcomes were renal function, weight loss, blood pressure, serum lipids and glycaemic control. We recruited 76 volunteers and 45 (35 men and 10 women) finished. There were no overall changes in renal function at 12 months and no significant differences in weight loss between groups (9.7 ± 2.9 kg and 6.6 ± 1.4 kg HPD and SPD group respectively; p = 0.32). Fasting blood glucose decreased significantly with no treatment effect. The decrease in HbA1c differed between treatments at 6 months (HPD −0.9 vs. SPD −0.3%; p = 0.039) but not at 12 months. HDL increased significantly with no treatment effects. There were no changes in LDL or blood pressure overall but DBP was lower in the HPD group (p = 0.024) at 12 months. ConclusionWeight loss improved overall metabolic control in this group of well controlled participants with type 2 diabetes regardless of diet composition.

Glucose uptake by the brain on chronic high-protein weight-loss diets with either moderate or low amounts of carbohydrate

Previous work has shown that hunger and food intake are lower in individuals on high-protein (HP) diets when combined with low carbohydrate (LC) intakes rather than with moderate carbohydrate (MC) intakes and where a more ketogenic state occurs. The aim of the present study was to investigate whether the difference between HPLC and HPMC diets was associated with changes in glucose and ketone body metabolism, particularly within key areas of the brain involved in appetite control. A total of twelve men, mean BMI 34·9 kg/m², took part in a randomised cross-over trial, with two 4-week periods when isoenergetic fixed-intake diets (8·3 MJ/d) were given, with 30% of the energy being given as protein and either (1) a very LC (22 g/d; HPLC) or (2) a MC (182 g/d; HPMC) intake. An ¹⁸fluoro-deoxyglucose positron emission tomography scan of the brain was conducted at the end of each dietary intervention period, following an overnight fast (n 4) or 4 h after consumption of a test meal (n 8). On the next day, whole-body ketone and glucose metabolism was quantified using [1,2,3,4-¹³C]acetoacetate, [2,4-¹³C]3-hydroxybutyrate and [6,6-²H₂]glucose. The composite hunger score was 14% lower (P= 0·013) for the HPLC dietary intervention than for the HPMC diet. Whole-body ketone flux was approximately 4-fold greater for the HPLC dietary intervention than for the HPMC diet (P< 0·001). The 9-fold difference in carbohydrate intakes between the HPLC and HPMC dietary interventions led to a 5% lower supply of glucose to the brain. Despite this, the uptake of glucose by the fifty-four regions of the brain analysed remained similar for the two dietary interventions. In conclusion, differences in the composite hunger score observed for the two dietary interventions are not associated with the use of alternative fuels by the brain.

Psychological well-being response to high protein and high carbohydrate weight loss diets in overweight and obese men: A randomised trial

Summary Background & aims High protein, low fat (HP) diets have established efficacy for weight management, but their effects on psychological well-being, particularly in men have not been well studied. This study compared an energy controlled HP diet with a high carbohydrate, low fat (HC) diet on psychological well-being after 1 year. Methods 117 obese men (mean ± SD, age 49.6 ± 9.2 years; BMI 31.2 ± 4.2 kg/m2) were randomised to consumption of either an energy restricted (∼7 MJ/day), HP diet (n = 57; 35% of total energy as protein, 40% carbohydrate, 25% fat) or an isocaloric, HC diet (n = 61; 17% protein, 58% carbohydrate, 25% fat) for 52 weeks. Body weight and psychological well-being was measured with Profile of Mood States (POMS), Bachman's Self Esteem scale and the SF-36 instruments at baseline (week 0), week 12 and week 52. Results Weight loss was (mean ± SEM) 8.9 ± 0.4 kg (8.6%) at Week 12 and 10.5 ± 0.8 kg (10.5%) at Week 52 (p Conclusions In overweight and obese men, weight loss on hypocaloric HP and HC diets were both effective in improving mood and general psychological well-being over one year. Registered under anzctr.org.au Identifier no. ACTRN 12606000002583.

Effect of a High Protein Weight Loss Diet on Weight, High-Sensitivity C-Reactive Protein, and Cardiovascular Risk among Overweight and Obese Women: A Parallel Clinical Trial

Studies regarding the effects of high protein (HP) diets on cardiovascular (CVD) risk factors have reported contradictory results. We aimed to determine the effects of an HP diet on CVD risk factors and high-sensitivity C-reactive protein (hs-CRP) among overweight and obese women. In this randomized controlled trial, we recruited 60 overweight and obese women, aged 20–65, into an HP or energy-restricted control diet for three months (protein, carbohydrate, and fat: 25%, 45%, and 30% versus 15%, 55%, and 30%, resp.). Total protein was divided between animal and plant sources in a 1 : 1 ratio, and animal sources were distributed equally between meats and dairy products. Fasting blood samples, hs-CRP, lipid profile, systolic and diastolic blood pressure, and anthropometric measurements were assessed using standard guidelines. Percent change was significantly different between the two diet groups for weight (standard protein (SP): −3.90 ± 0.26 versus HP: −6.10 ± 0.34%; P < 0.0001, resp.) and waist circumference (SP: −3.03 ± 0.21 versus HP: −5.06 ± 0.28%; P < 0.0001, resp.). Percent change of fasting blood glucose (FBG) substantially decreased in the control group compared to the HP group (−9.13 ± 0.67 versus −4.93 ± 1.4%; P = 0.01, resp.). Total cholesterol, systolic blood pressure (SBP), and diastolic blood pressure (DBP) decreased both in the HP and in the control diet groups (P = 0.06, P = 0.07, and P = 0.09, resp.); however, the results were marginally significant. Serum levels of hs-CRP were reduced both in the control (−0.08 ± 0.11%, P = 0.06) and in the high protein groups (−0.04 ± 0.09%, P = 0.06). The energy-restricted HP diet resulted in more beneficial effects on weight loss and reduction of waist circumference. CVD risk factors may improve with HP diets among overweight and obese women. When using isoenergetic weight loss diets, total cholesterol, hs-CRP, and SBP were marginally significantly reduced, independent of dietary protein content. This trial is registered with ClinicalTrials.gov NCT01763528.

Diet Composition Is Associated with Endogenous Formation of N-Nitroso Compounds in Obese Men1–3

Endogenous formation of carcinogenic N-nitroso compounds (NOC) occurs in the human gut. Red meat is considered the most important dietary component linked to NOC formation, although nitrate and vitamin C (VitC) also contribute. We previously showed that high-protein weight-loss diets increased fecal NOC and this was enhanced by simultaneous carbohydrate restriction. Although previous studies have focused on the effect of either 1 or 2 dietary components on endogenous NOC formation, no study to date has investigated the combined contribution of various dietary components. The current study therefore assessed the joint impact of several known dietary contributors to the endogenous formation of NOC in obese men. It also aimed to identify further novel contributors and investigate their role in explaining shifts in endogenous formation of NOC. Three dietary trials were conducted in obese men consuming body weight maintenance or weight-loss diets, with NOC measured in fecal samples. Consumption of meat-based weight-loss diets increased (P < 0.001) fecal NOC. Red meat intake was positively correlated with the fecal log NOC concentration (r = 0.60; P < 0.001). Dietary carbohydrate and sugar were negatively correlated with the fecal log NOC concentration (r = -0.66 for both; P < 0.001). Multiple regression analysis identified several dietary components that drive endogenous NOC formation, namely, red meat, nitrate, VitC, total energy, and nonstarch polysaccharides. We present a regression model that predicts endogenous NOC formation in obese men based on their dietary intakes. This model could improve the estimation of endogenous NOC formation, currently used in epidemiological studies into diet and cancer.

Comparative effects of low-carbohydrate high-protein versus low-fat diets on the kidney.

Concerns exist about deleterious renal effects of low-carbohydrate high-protein weight loss diets. This issue was addressed in a secondary analysis of a parallel randomized, controlled long-term trial. Between 2003 and 2007, 307 obese adults without serious medical illnesses at three United States academic centers were randomly assigned to a low-carbohydrate high-protein or a low-fat weight-loss diet for 24 months. Main outcomes included renal filtration (GFR) indices (serum creatinine, cystatin C, creatinine clearance); 24-hour urinary volume; albumin; calcium excretion; and serum solutes at 3, 12, and 24 months. Compared with the low-fat diet, low-carbohydrate high-protein consumption was associated with minor reductions in serum creatinine (relative difference, -4.2%) and cystatin C (-8.4%) at 3 months and relative increases in creatinine clearance at 3 (15.8 ml/min) and 12 (20.8 ml/min) months; serum urea at 3 (14.4%), 12 (9.0%), and 24 (8.2%) months; and 24-hour urinary volume at 12 (438 ml) and 24 (268 ml) months. Urinary calcium excretion increased at 3 (36.1%) and 12 (35.7%) months without changes in bone density or clinical presentations of new kidney stones. In healthy obese individuals, a low-carbohydrate high-protein weight-loss diet over 2 years was not associated with noticeably harmful effects on GFR, albuminuria, or fluid and electrolyte balance compared with a low-fat diet. Further follow-up is needed to determine even longer-term effects on kidney function.

Safety and efficacy of high-protein diets for weight loss

Dietary strategies that can help reduce hunger and promote fullness are beneficial for weight control, since these are major limiting factors for success. High-protein (HP) diets, specifically those that maintain the absolute number of grams ingested, while reducing energy, are a popular strategy for weight loss (WL) due to the effects of protein-induced satiety to control hunger. Nonetheless, both the safety and efficacy of HP WL diets have been questioned, particularly in combination with low-carbohydrate advice. Nonetheless, for short-to-medium-term intervention studies (over several months), increasing the energetic contribution of protein does appear effective. The effects of HP diets on appetite, bone health, renal function, blood pressure, cardiovascular bio-markers, antioxidant status, gut health and psychological function are discussed. Further research is warranted to validate the physiological effects of HP diets over longer periods of time, including studies that modify the quality of macronutrients (i.e. the type of carbohydrate, fat and protein) and the interaction with other interventions (e.g. exercise and dietary supplements).

The effect of modifying dietary protein and carbohydrate in weight loss on arterial compliance and postprandial lipidemia in overweight women with polycystic ovary syndrome

In overweight women with polycystic ovary syndrome, weight loss improves arterial compliance and postprandial lipidemia. Modifying dietary carbohydrate or protein in weight loss provided similar improvements in arterial compliance and postprandial lipidemia.

Energy Expenditure Does not Differ, but Protein Oxidation Rates Appear Lower in Meals Containing Predominantly Meat versus Soy Sources of Protein

Background: High protein meals produce 3 relevant effects in weight management: i) higher thermogenic cost, ii) enhanced fat oxidation, and iii) greater satiation. Pork has been reported to be more thermogenic than soy, suggesting meat protein may be superior to plant protein in a high-protein weight loss diet context. In this study, we aimed to compare the effects of high-protein meals using meat, dairy, and soy sources respectively. Methods: This crossover feeding trial measured energy expenditure, substrate oxidation, and satiety levels of 12 adults during 8-hour stays in a whole-room calorimeter. The 3 isoenergetic high-protein test meals (30% protein, 40% carbohydrate, 30% fat) contained predominantly meat, dairy, and soy protein. Results: There was no significant difference between meals for effects on energy expenditure (p = 0.987), carbohydrate oxidation (p = 0.951), and fat oxidation (p = 0.997). Protein oxidation was significantly lower in meals with predominantly meat compared to soy sources (p = 0.012). There was no significant difference between meals for reported satiety levels (p = 0.296). Conclusion: High-protein meals may be argued as beneficial for weight loss. Animal protein does not appear to offer superior energy expenditure effects, but there may be protein-sparing effects with meat, which may be beneficial in terms of retaining lean body mass.

High protein diets decrease total and abdominal fat and improve CVD risk profile in overweight and obese men and women with elevated triacylglycerol

Background and aims It is unclear whether high protein weight loss diets have beneficial effects on weight loss, abdominal fat mass, lipids, glucose and insulin compared to conventional low fat diets in subjects at increased risk of cardiovascular disease (CVD) because of elevated glucose and triglyceride concentrations. Our objective was to determine the effects of high protein (HP) compared to standard protein (SP) diets on CVD risk in obese adults. Methods and results Data from three, 12 week, randomized parallel trials with subjects assigned to either HP or SP diet (5500–6500 kJ/day) were pooled. Weight, body composition (dual energy X-ray absorptiometry), lipids, insulin and glucose were measured before and after weight loss. Data from 215 subjects (49.9 ± 9.8 years, BMI 33.5 ± 3.7 kg/m 2), 108 HP, 107 SP were analyzed. Weight loss (HP diet 7.82 ± 0.37 kg; SP diet 7.65 ± 0.39 kg, NS) and total fat loss were not different (HP 6.8 ± 4.3 kg; LP 6.4 ± 4.7 kg, NS on intention to treat analysis). The reduction in triacylglycerol (TAG) was greater on HP than SP 0.48 ± 0.07 mmol/L vs 0.27 ± 0.06 mmol/L, ( P < 0.001). Subjects with TAG greater than the median (>1.54 mmol/L at baseline) lost more weight (HP 8.5 ± 0.6; SP 6.9 ± 0.6 kg, P = 0.01, diet by TG group), total (HP 6.17 ± 0.50 kg; SP 4.52 ± 0.52 kg, P = 0.007) and abdominal fat (HP 1.92 ± 0.17 kg; SP 1.23 ± 0.19 kg, P = 0.005) on HP. Total cholesterol (12 vs 6%, HP vs SP) and TAG (39 vs 20%, HP vs SP) decreased to a greater extent in these subjects (both P ≤ 0.05) on HP. Conclusion Short-term high protein weight loss diets had beneficial effects on total cholesterol and triacylglycerol in overweight and obese subjects and achieved greater weight loss and better lipid results in subjects at increased risk of CVD. These observations provide further information regarding the utility of this dietary approach in effectively managing body weight and composition and reducing CVD risk in overweight and obese individuals.

Benefits of high-protein weight loss diets: enough evidence for practice?

Benefits of high-protein weight loss diets: enough evidence for practice?

Benefits of high-protein weight loss diets: enough evidence for practice?

High-protein diets, often with carbohydrate restriction, are quite popular among overweight Americans pursuing strategies for weight control. Recently, well designed clinical trials have evaluated the anthropometric and metabolic effects of these diets. This review focuses on the impact of high-protein diets on energy expenditure and satiety; the diets' effects on weight loss, body composition, cardiovascular risk, and glycemic control; and potential detrimental consequences of high-protein intake. Current evidence indicates that protein-induced energy expenditure and satiety contribute to weight control. Randomized, controlled trials continue to show comparable, if not superior, effects of high-protein diets compared with lower protein diets on weight loss, preservation of lean body mass, and improvement in several cardiovascular risk factors for up to 12 months. Evidence that chronic high-protein intake affects glucose metabolism is inconclusive at present. Further study of the long-term safety of diets with varying amounts of protein is warranted. On the basis of patients' metabolic profiles and preferences, practitioners can recommend individualized, nutrient-rich diets within current nutritional guidelines for weight control. Diets moderately increased in protein and modestly restricted in carbohydrate and fat, particularly saturated fat, may have beneficial effects on body weight, body composition, and associated metabolic parameters. Key issues must be resolved regarding the long-term compliance and safety of chronic high-protein intake.

Factors Influencing Body Mass Index, Appetite Control, and the Role of Glutamate and Excess Nutritional Protein During Child Development: A Review

Obesity has become a major public health concern in this century. Yet, the widespread popularisation in managing overweight and obesity indicates that the problem of body weight maintenance has developed from an only medical into an interdisciplinary and already political problem. Current ideas about lifestyle and strategies to maintain health and weight have become dominated by increasingly popular beliefs that contrast scientific evidence. Particularly the relationship between physical activity, energy intake and body mass index (BMI) explains markedly less of the within-population variance of the BMI than commonly assumed. Instead, it has been noted that protein consumption significantly correlates with BMI explaining up to 13% of the BMI variance in young adolescents. Increasing evidence suggests that nutritional protein can stimulate food intake. Serum levels of most amino acids increase following a protein rich meal. Regions of the brain that are involved in the regulation of appetite accumulate glutamate and other small molecules. Free glutamate can be toxic for some of the essential neuronal structures of hypothalamic appetite regulation, may impair satiety and result in voracity. Protein toxicity in humans occurs at amounts beyond an intake of 200 g/d. Protein intake needs supplementation either by carbohydrate or fat in order to reduce its contribution to total energy intake to less than 40%, and the protein content of many popular high-protein weight loss diets must for the same reasons be regarded with great caution, and should particularly be avoided during pregnancy and childhood.