New information could change our thinking about the maximum safe amount, but until we know more about the safety, risks and benefits of high protein diets, this seems like a reasonable recommendation. As a service to our readers, Harvard Health Publishing provides access to our library of archived content. Please note the date of last review or update on all articles.
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Get helpful tips and guidance for everything from fighting inflammation to finding the best diets for weight loss Stay on top of latest health news from Harvard Medical School. Recent Blog Articles. Why is topical vitamin C important for skin health? Preventing preeclampsia may be as simple as taking an aspirin. While incretin mimetics do promote weight loss, the effect of DPP-4 inhibitors on weight control is less clear.
Nevertheless, pharmacological inhibition of DPP-4 activity may be a strategy to decrease appetite and improve the condition of typediabetes. Inhibition of DPP-4 activity by certain foods is therefore of great importance for medical nutrition therapy. It was suggested by the authors that after luminal degradation, the IPA fragments may act in situ as competitive inhibitors of DPP-4 as it cleaves peptides with an N-terminal alanine or proline amino acid residue [ 43 ], suggesting a similar, albeit more modest, effect as pharmacological DPP-4 inhibitors such as Sitagliptin.
Increased incretin levels mediate postprandial insulin release, thereby inducing satiety [ 44 ] and the preference for food-related cues [ 45 ]. The secretion of gut neuropeptides that induce satiation, GLP-1, CCK, and peptide YY PYY seem to be increased in response to a high-protein diet whereas concentrations of orexigenic hormones such as ghrelin seem to be reduced [ 46 , 47 ].
Enteroendocrine cells which release GLP-1 and GIP are in direct contact with the gut lumen and by this means seem to be able to sense arrival and passage of nutrients along the gastrointestinal tract. It has to be noted, however, that GLP-1 secretion is nutrient related increased after a protein meal in combination with CHOs [ 49 ]. Increased GLP-1 concentrations were also found in men after a high protein breakfast, lunch and dinner [ 50 ].
A study in humans by Blom et al. It is very likely that increased protein-induced satiety leads to reduced subsequent energy intake which is beneficial for weight loss. This effect is not related to a conditioned taste aversion. A decreased gastric emptying rate following a high-protein diet has also been observed [ 52 ].
High-protein diets may directly promote a satiety response. In the aminostatic hypothesis was introduced: increased serum amino acid concentrations produced feelings of satiety whereas decreasing concentrations created feelings of hunger [ 53 ]. Diets high in protein will elevate concentrations of plasma amino acids [ 54 ]. According to Nefti et al. Poppitt et al. Along these lines, Westerterp-Plantenga [ 26 ] found a significant increase in h satiety in subjects consuming a high-protein diet compared to a high-fat diet.
The aminostatic hypothesis has been supported by several, but not all studies [ 57 ], showing that high-protein diets result in higher levels of satiety, however, complex homeostatic mechanisms between the peripheral organs and the central nervous system which cause the aminostatic effect are not yet fully understood.
More research in this area is necessary to elucidate this hypothesis. Alteration of gluconeogenesis has been found to contribute to satiety [ 58 ]. High-protein and low-carbohydrate diets promote hepatic gluconeogenesis to maintain plasma glucose levels. Two key enzymes of gluconeogenesis, phosphoenolpyruvate carboxykinase PEPCK and glucosephosphatase G6P , are upregulated in rats fed a high-protein diet, suggesting that gluconeogenesis is stimulated by a high-protein diet [ 59 ].
A modulation of hepatic gluconeogenesis and increased glucose homeostasis could be responsible for the satiating effect in this animal model [ 60 ]. A recent study in humans found an increased gluconeogenesis following high-protein intake but this increase was unrelated to appetite suppression [ 62 ]. Instead, the authors observed an increased production of ketone bodies especially beta-hydroxybutyrate in response to the high-protein diet.
The increased concentration of beta-hydroxybutyrate may act as an appetite suppressing substrate [ 62 ]. The latter may be most important in contributing to increased satiety, especially if the diet is high in protein and low in CHOs. It is also well established that a decreasing level of blood glucose is an appetite stimulating state whereas amino-acid induced gluconeogenesis acts as appetite suppressant preventing hypoglycemia. Central mechanisms include augmented activation of Pro-opiomelanocortin POMC neurons and alpha-melanocyte-stimulating hormone and decreased activation of non-POMC neurons upon acute ingestion of a high-protein diet.
Intraduodenal protein can activate vagal afferent fibers and after high-protein ingestion c-Fos expression in neurons of the nucleus of the solitary tract was increased [ 58 ]. High-protein diets can help preserve lean body mass during weight loss.
Mettler et al. Performance parameters were not affected in the subjects, most likely due to the short study period. In this study, the authors balanced energy by changing fat intake and not carbohydrate intake as is usually the case.
Glucose intake leads to post-prandial insulin secretion. The inhibitory effect of insulin on lipolysis in adipose tissue leads to the postprandial suppression of fat oxidation [ 64 ]. This inverse relationship between dietary carbohydrate intake and fat oxidation may explain why Mettler did not observe differences in fat loss between groups whereas others observed reductions in fat mass in non-athletic, overweight subjects on a high-protein low-carbohydrate diet [ 65 , 66 ].
Table 2 shows examples of foods high in protein relative to their carbohydrate and fat content. With regard to the macronutrient distribution, it appears that there is a difference whether protein is increased at the expense of CHO or fat. Increasing protein at the expense of CHOs leads to increased contribution of amino acids to energy expenditure with a concomitant decrease in lipogenesis due to decreased supply of dietary glucose [ 68 ] and likely has a negative impact on exercise performance and training intensity [ 69 ].
Carbohydrate supply is critical for strength and endurance performance. Athletes should therefore be aware about limited energy intake and maintenance of training levels. For obese subjects, lowering carbohydrate in favor of protein might be advantageous as dietary CHOs might impair fat oxidation [ 70 ] whereas low-CHO, high-protein diets reduce adipose tissue development [ 71 ]. Higher daily protein intake at the expense of fat intake could substantially reduce total energy intake, which could possibly translate to a healthier weight status [ 72 ].
Long-term effects of high-protein diets depend on the population studied as well as the exact composition of the diet but have generally been shown to include weight reduction and weight loss maintenance as well as beneficial effects on metabolic risk factors such total cholesterol and triacylglycerol.
Claessens et al. The authors conclude that after 12 weeks of diet intervention, the low-fat, high-protein diet was more effective for weight control. Clifton et al. The authors conclude that subjects in the high-protein group had beneficial effects on total cholesterol and triacylglycerol and achieved greater weight loss and better lipid results. In another study, Clifton et al.
The authors found no significant difference between groups regarding weight loss. Protein intake in grams derived from the dietary records, however, was directly related to weight loss [ 75 ]. Westerterp-Plantenga et al. The mechanisms by which increased long-term dietary protein intake regulate body weight are not well understood but are most likely multifactorial.
Depending on the diet, lower triacylglycerol levels and hence fat mass loss with a higher-protein diet as well as increased satiety possibly mediated by increased leptin sensitivity have been discussed [ 75 , 78 , 79 ]. Fluid loss related to reduced carbohydrate intake and overall caloric restriction have also been discussed to mediate weight loss [ 5 ]. Metabolomics studies revealed that high intake of branched-chain amino acids BCAAs, Valine, Leucine, Isoleucine and aromatic amino acids Phenylalanine, Tyrosine may be associated with the development of metabolic diseases [ 80 ].
Importantly, this only occurs in combination with a high-fat diet. High catabolic flux of these intermediates interferes with appropriate oxidation of fatty acids, possibly by allosteric inhibition of citrate synthase [ 81 ] which slows down the TCA cycle, causing buildup of incompletely oxidized substrates such as acylcarnitines.
This accumulation leads to mitochondrial stress, impaired insulin action, and finally to perturbation of glucose homeostasis [ 80 ]. This connection might be highly relevant as many overweight people worldwide are effectively on a high-fat diet but might as well do weight-training and supplement with BCAAs.
Therefore, in people with a high caloric intake from fat BCAA supplementation might exacerbate the risk of metabolic disease. Diets high in protein pose a potential acid load to the kidneys, mainly as sulfates and phosphates [ 82 ]. It was hypothesized that calcium and hence bone mass was lost in order to buffer this acid load [ 83 ].
Although the bone-loss hypothesis has been refuted and there is agreement that high-protein diets are actually favorable to intestinal calcium uptake, bone health and bone mineral density [ 84 ], the protein-induced acid-load to the kidneys remains, e.
This phenomenon is especially prominent in diets such as the Atkins diet which can lead to additional acid buildup from ketone bodies in response to reduced carbohydrates and concomitantly increased fat and protein intake. Frank et al. They reported significant changes in the glomerular filtration rate, the filtration fraction, albuminuria, serum uric acid, and urinary pH values in the high-protein diet group.
The authors conclude that renal hemodynamics and renal excretion is altered in response to a short-term, high-protein diet. Although depended on the source of protein, interventional studies in humans have shown that high-protein diets have the potential to increase the risk of calcium stone-formation in the urinary tract [ 82 , 86 ]. In order to maintain an acid—base balance in the body, people on a high-protein diet should consider ingestion of alkali buffers such as fruits and vegetables high in potassium alkaline-forming foods.
Glutamine or sodium bicarbonate supplements can also help to restore acid—base balance in the body. In general, people experimenting with high-protein diets are advised to monitor their renal function.
People on high-protein diets are advised to choose their source of protein very carefully i. Many protein-rich foods of animal origin e. This may put consumers of high-protein diets at higher risk for heart disease, hyperlipidemia and hypercholesterolemia [ 87 ].
Healthier proteins from vegetables soy protein, beans, tofu, seitan or nuts or fish could be a valuable alternative. Finally, all excess protein will eventually be converted to glucose via gluconeogenesis or ketone bodies [ 88 , 89 ]. Protein requirements differ depending on age and activity levels. For infants and children the RDA is higher. However, when compared to total energy intake the protein RDA for infants and children is similar to that for adults.
Approximately 10 to 35 percent of your total daily calorie intake should come from protein. Most people consume adequate amounts of protein in their daily diets. However, how well children grow and how well adults maintain their health depends largely on the quality of the protein consumed. Complete proteins, or high-quality proteins, contain all the essential amino acids essential for tissue growth and repair.
Sources of complete proteins include eggs, milk, meat, fish and poultry. Even athletes are often getting more protein than they need, without supplements, because their calorie requirements are higher.
And with more food comes more protein. Wempen explains extra protein intake also can lead to elevated blood lipids and heart disease, because many high-protein foods are high in total fat and saturated fat.
Extra protein intake, which can tax the kidneys, poses an additional risk to individuals predisposed to kidney disease. Anywhere from 10 to 35 percent of your calories should come from protein. The recommended dietary allowance to prevent deficiency for an average sedentary adult is 0. For example, a person who weighs 75 kilograms pounds should consume 60 grams of protein per day.
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