High-protein diets in hyperlipidemia: effect of wheat gluten on serum lipids, uric acid, and renal function

Metabolic effects of high-protein diets

Protein is more satiating than carbohydrate or fat, and high-protein diets (25%-35% of energy) are commonly used for weight loss. High-protein diets usually replace carbohydrate with protein and may be low or high in saturated fat. Invariably, serum triglyceride is lower with the lower intake of carbohydrate, but the effects on high-density lipoprotein cholesterol and low-density lipoprotein cholesterol are strongly dependent on the amount of carbohydrate restriction and the intake of saturated fat, and in some cases low-density lipoprotein cholesterol may rise despite weight loss. In situations of weight stability, higher intakes of protein are associated with lower blood pressures, and in diabetic patients higher intakes of protein are associated with lower glycosylated hemoglobin. The overall effect on long-term atherosclerosis risk is not clear, as the current limited epidemiology provides conflicting data.

Almonds reduce biomarkers of lipid peroxidation in older hyperlipidemic subjects

Nut consumption has been associated with reduced coronary heart disease (CHD) risk. In addition to cholesterol-lowering properties, almonds have been shown to lower oxidized LDL concentrations. However, little is known regarding their effects on other markers of oxidative stress. The dose-response effects of whole almonds, taken as snacks, were compared with low-saturated fat (<5% energy) whole-wheat muffins (control) in the therapeutic diets of hyperlipidemic subjects. In a randomized crossover study, 27 hyperlipidemic men and women consumed 3 isoenergetic (mean 423 kcal/d or 1770 kJ/d) supplements each for 1 mo. Supplements consisted of full-dose almonds (73 +/- 3 g/d), half-dose almonds plus half-dose muffins (half-dose almonds), and full-dose muffins (control). Subjects were assessed at wk 0, 2 and 4. Mean body weights differed < or = 300 g between treatments, although the weight loss on the half-dose almond treatment was greater than on the control (P < 0.01). At 4 wk, the full-dose almonds reduced serum concentrations of malondialdehyde (MDA) (P = 0.040) and creatinine-adjusted urinary isoprostane output (P = 0.026) compared with the control. Serum concentrations of alpha- or gamma-tocopherol, adjusted or unadjusted for total cholesterol, were not affected by the treatments. Almond antioxidant activity was demonstrated by their effect on 2 biomarkers of lipid peroxidation, serum MDA and urinary isoprostanes, and supports the previous finding that almonds reduced oxidation of LDL-C. Antioxidant activity provides an additional possible mechanism, in addition to lowering cholesterol, that may account for the reduction in CHD risk with nut consumption.

Are High-Protein, Vegetable-Based Diets Safe for Kidney Function? A Review of the Literature

In individuals with chronic kidney disease, high-protein diets have been shown to accelerate renal deterioration, whereas low-protein diets increase the risk of protein malnutrition. Vegetarian diets have been promoted as a way to halt progression of kidney disease while maintaining adequate nutrition. We review the literature to date comparing the effects of animal and vegetable protein on kidney function in health and disease. Diets with conventional amounts of protein, as well as high-protein diets, are reviewed. The literature shows that in short-term clinical trials, animal protein causes dynamic effects on renal function, whereas egg white, dairy, and soy do not. These differences are seen both in diets with conventional amounts of protein and those with high amounts of protein. The long-term effects of animal protein on normal kidney function are not known. Although data on persons with chronic kidney disease are limited, it appears that high intake of animal and vegetable proteins accelerates the underlying disease process not only in physiologic studies but also in short-term interventional trials. The long-term effects of high protein intake on chronic kidney disease are still poorly understood. Several mechanisms have been suggested to explain the different effects of animal and vegetable proteins on normal kidney function, including differences in postprandial circulating hormones, sites of protein metabolism, and interaction with accompanying micronutrients.

Protein, body weight, and cardiovascular health

Widespread popularity of high-protein diets has drawn controversy as well as scientific interest. By reducing intake of carbohydrates and increasing consumption of fats and proteins, such diets are thought to increase satiety, facilitate weight loss, and improve cardiovascular risk factors. In recent years, many randomized controlled studies have compared the effects of higher-protein diets on weight loss and cardiovascular risk factors with those of lower-protein diets. The aim of this review was to provide an overview of experimental and epidemiologic evidence regarding the role of protein in weight loss and cardiovascular risk. Emerging evidence from clinical trials indicates that higher-protein diets increase short-term weight loss and improve blood lipids, but long-term data are lacking. Findings from epidemiologic studies show a significant relationship between increased protein intake and lower risk of hypertension and coronary heart disease. However, different sources of protein appear to have different effects on cardiovascular disease. Although optimal amounts and sources of protein cannot be determined at this time, evidence suggests a potential benefit of partially replace refined carbohydrates with protein sources low in saturated fats.

Dietary protein type and cardiovascular disease risk factors

Observational studies suggested a negative association between vegetable protein and cardiovascular disease risk, whereas intervention studies have been less consistent. The majority of interventional studies that have evaluated the effects of soy protein compared to animal protein have used casein. Relative to casein, the effect of soy protein on lipids and lipoprotein appears to be variable and less dramatic than originally reported. When compared to animal proteins other than casein, relatively large intakes of soy protein (>/=25 g/d) appear to have a consistent, albeit small ( asymptotically equal to 5%), hypocholesterolemic effect. When assessed, no consistent additional benefit of soy protein on other cardiovascular disease risk factors; Lp(a), inflammatory markers, biomarkers of oxidative stress and endothelial function, has been reported. The data available on the effect of dietary protein on plasma lipids, lipoprotein levels, and cardiovascular disease risk factors is difficult to interpret and insufficient to account for the discrepancy between the observational and interventional studies.

The effects of high protein diets on thermogenesis, satiety and weight loss: a critical review

For years, proponents of some fad diets have claimed that higher amounts of protein facilitate weight loss. Only in recent years have studies begun to examine the effects of high protein diets on energy expenditure, subsequent energy intake and weight loss as compared to lower protein diets. In this study, we conducted a systematic review of randomized investigations on the effects of high protein diets on dietary thermogenesis, satiety, body weight and fat loss. There is convincing evidence that a higher protein intake increases thermogenesis and satiety compared to diets of lower protein content. The weight of evidence also suggests that high protein meals lead to a reduced subsequent energy intake. Some evidence suggests that diets higher in protein result in an increased weight loss and fat loss as compared to diets lower in protein, but findings have not been consistent. In dietary practice, it may be beneficial to partially replace refined carbohydrate with protein sources that are low in saturated fat. Although recent evidence supports potential benefit, rigorous longer-term studies are needed to investigate the effects of high protein diets on weight loss and weight maintenance.

Serum uric acid in traditional Pacific Islanders and in Swedes

BACKGROUND

In some western populations, increased serum uric acid has been positively associated with cardiovascular disease, possibly because hyperuricaemia could be an untoward part of the insulin-resistant metabolic syndrome. However, there is evidence that uric acid is a free radical scavenger capable of inhibiting LDL oxidation. Amongst the traditional horticulturalists of Kitava, Trobriand Islands, Papua New Guinea, cardiovascular disease, hypertension, hyperinsulinaemia and abdominal obesity are absent or rare. In contrast, serum triglycerides are similar to Swedish levels.

OBJECTIVE

To compare serum uric acid between nonwesternized and westernized populations.

METHODS

Fasting levels of serum uric acid were measured cross-sectionally in 171 Kitavans aged 20-86 years and in 244 randomly selected Swedish subjects aged 20-80 years.

RESULTS

There were small differences in serum uric acid between the two populations, although a slight increase with age was found only in Swedish males (r = 0.20; P = 0.03) and females (r = 0.36; P < 0.0001). Above 40 years of age, uric acid was approximately 10% lower in Kitavans, a difference which was statistically significant only in males, possibly because of the limited number of females. Regarding hyperuricaemia, two Kitavan males had uric acid above 450 micromol L-1 whilst none of the females was above 340 micromol L-1. Amongst the Swedish subjects, five of 117 males and 19 of 127 females had hyperuricaemia according to these definitions.

CONCLUSION

The rather similar uric acid levels between Kitava and Sweden imply that uric acid is of minor importance to explain the apparent absence of cardiovascular disease in Kitava.

An increase in dietary protein improves the blood glucose response in persons with type 2 diabetes

BACKGROUND

In single-meal studies, dietary protein does not result in an increase in glucose concentrations in persons with or without type 2 diabetes, even though the resulting amino acids can be used for gluconeogenesis.

OBJECTIVE

The metabolic effects of a high-protein diet were compared with those of the prototypical healthy (control) diet, which is currently recommended by several scientific organizations.

DESIGN

The metabolic effects of both diets, consumed for 5 wk each (separated by a 2-5-wk washout period), were studied in 12 subjects with untreated type 2 diabetes. The ratio of protein to carbohydrate to fat was 30:40:30 in the high-protein diet and 15:55:30 in the control diet. The subjects remained weight-stable during the study.

RESULTS

With the fasting glucose concentration used as a baseline from which to determine the area under the curve, the high-protein diet resulted in a 40% decrease in the mean 24-h integrated glucose area response. Glycated hemoglobin decreased 0.8% and 0.3% after 5 wk of the high-protein and control diets, respectively; the difference was significant (P < 0.05). The rate of change over time was also significantly greater after the high-protein diet than after the control diet (P < 0.001). Fasting triacylglycerol was significantly lower after the high-protein diet than after the control diet. Insulin, C-peptide, and free fatty acid concentrations were not significantly different after the 2 diets.

CONCLUSION

A high-protein diet lowers blood glucose postprandially in persons with type 2 diabetes and improves overall glucose control. However, longer-term studies are necessary to determine the total magnitude of response, possible adverse effects, and the long-term acceptability of the diet.

Plant-based foods and prevention of cardiovascular disease: an overview

Evidence from prospective cohort studies indicates that a high consumption of plant-based foods such as fruit and vegetables, nuts, and whole grains is associated with a significantly lower risk of coronary artery disease and stroke. The protective effects of these foods are probably mediated through multiple beneficial nutrients contained in these foods, including mono- and polyunsaturated fatty acids, n-3 fatty acids, antioxidant vitamins, minerals, phytochemicals, fiber, and plant protein. In dietary practice, healthy plant-based diets do not necessarily have to be low in fat. Instead, these diets should include unsaturated fats as the predominant form of dietary fat (eg, fats from natural liquid vegetable oils and nuts), whole grains as the main form of carbohydrate, an abundance of fruit and vegetables, and adequate n-3 fatty acids. Such diets, which also have many other health benefits, deserve more emphasis in dietary recommendations to prevent chronic diseases.

A low-iron-available, polyphenol-enriched, carbohydrate-restricted diet to slow progression of diabetic nephropathy

Diabetic nephropathy has become the leading cause of uremia. Several lines of evidence suggest dietary factors other than protein intake have a substantial role in the progression of diabetic nephropathy to end-stage renal disease. The present investigation was initiated to evaluate whether a carbohydrate-restricted, low-iron-available, polyphenol-enriched (CR-LIPE) diet may delay and improve the outcome of diabetic nephropathy to a greater extent than standard protein restriction. To this aim, 191 diabetic patients, all with type 2 diabetes, were randomized to either CR-LIPE or standard protein restriction and the following outcomes monitored: doubling of serum creatinine, cumulative incidence of end-stage renal disease, and all cause mortality. Over a mean follow-up interval of 3.9 +/- 1.8 years, serum creatinine concentration doubled in 19 patients on CR-LIPE (21%) and in 31 control subjects (39%) (P < 0.01). Renal replacement therapy or death occurred in 18 patients on CR-LIPE (20%) and in 31 control subjects (39%) (P < 0.01). These differences were independent from follow-up interval, sex, mean arterial blood pressure, HbA(1c), initial renal dysfunction, and angiotensin system inhibitor use. In conclusion, CR-LIPE was 40-50% more effective than standard protein restriction in improving renal and overall survival rates.

Effect of high vegetable protein diets on urinary calcium loss in middle-aged men and women

OBJECTIVE

To determine the effect of high-protein diets, which have recently been promoted for their health benefits, on urinary calcium losses and bone turnover in older subjects.

DESIGN

Randomized controlled cross-over study.

SETTING

Teaching hospital and university.

SUBJECTS

Twenty hyperlipidemic men and postmenopausal women (age 56+/-2 y) completed the study.

INTERVENTION

One-month test and control phases during which subjects consumed equi-energy metabolic diets high in calcium (1578 and 1593 mg/day, respectively). On the test diet 11% of total dietary energy from starch in the control bread was replaced by protein (wheat gluten), resulting in 27% of energy from protein on the test diet vs 16% on the control diet.

MAIN OUTCOME MEASURE

Urinary calcium excretion.

RESULTS

Compared with the control diet, at week 4, the test diet increased mean (+/-s.e.m.) 24 h urinary output of calcium (139+/-15 vs 227+/-21 mg, P=0.004). The treatment difference in urinary calcium loss correlated with the serum anion gap as a marker of metabolic acid production (r=0.57, P=0.011). Serum calcium levels were marginally lower 2.41+/-0.02 vs 2.38+/-0.02 mmol/l (P=0.075), but there was no significant treatment difference in calcium balance, possibly related to the high background calcium intake on both diets.

CONCLUSION

In the presence of high dietary calcium intakes the vegetable protein gluten does not appear to have a negative effect on calcium balance despite increased urinary calcium loss.

Dose response of almonds on coronary heart disease risk factors: blood lipids, oxidized low-density lipoproteins, lipoprotein(a), homocysteine, and pulmonary nitric oxide: a randomized, controlled, crossover trial

BACKGROUND

Although recent studies have indicated that nut consumption may improve levels of blood lipids, nuts are not generally recommended as snacks for hyperlipidemic subjects because of their high fat content. Furthermore, the effective dose is still unknown.

METHODS AND RESULTS

The dose-response effects of whole almonds, taken as snacks, were compared with low-saturated fat (<5% energy) whole-wheat muffins (control) in the therapeutic diets of hyperlipidemic subjects. In a randomized crossover study, 27 hyperlipidemic men and women consumed 3 isoenergetic (mean 423 kcal/d) supplements each for 1 month. Supplements provided 22.2% of energy and consisted of full-dose almonds (73+/-3 g/d), half-dose almonds plus half-dose muffins, and full-dose muffins. Fasting blood, expired air, blood pressure, and body weight measurements were obtained at weeks 0, 2, and 4. Mean body weights differed <300 g between treatments. The full-dose almonds produced the greatest reduction in levels of blood lipids. Significant reductions from baseline were seen on both half- and full-dose almonds for LDL cholesterol (4.4+/-1.7%, P=0.018, and 9.4+/-1.9%, P<0.001, respectively) and LDL:HDL cholesterol (7.8+/-2.2%, P=0.001, and 12.0+/-2.1%, P<0.001, respectively) and on full-dose almonds alone for lipoprotein(a) (7.8+/-3.5%, P=0.034) and oxidized LDL concentrations (14.0+/-3.8%, P<0.001), with no significant reductions on the control diet. No difference was seen in pulmonary nitric oxide between treatments.

CONCLUSIONS

Almonds used as snacks in the diets of hyperlipidemic subjects significantly reduce coronary heart disease risk factors, probably in part because of the nonfat (protein and fiber) and monounsaturated fatty acid components of the nut.

A soy protein diet alters hepatic lipid metabolism gene expression and reduces serum lipids and renal fibrogenic cytokines in rats with chronic nephrotic syndrome

Nephrotic syndrome (NS) is characterized by the presence of proteinuria and hyperlipidemia. However, ingestion of soy protein has a hypolipidemic effect. The present study was designed to determine whether the ingestion of a 20% soy protein diet regulates the expression of hepatic sterol regulatory element binding protein (SREBP)-1, fatty acid synthase (FAS), malic enzyme, beta-hydroxy-beta-methylglutaryl-CoA (HMG-CoA) reductase (r) and synthase (s), and LDL receptor (r), and to assess whether soy protein improves lipid and renal abnormalities in rats with chronic NS. Male Wistar rats were injected with vehicle or with puromycin aminonucleoside to induce NS and were fed either 20% casein or soy protein diets for 64 d. NS rats fed 20% soy protein had improved creatinine clearance and reduced proteinuria, hypercholesterolemia, hypertriglyceridemia, as well as VLDL-triglycerides and LDL cholesterol compared with NS rats fed the 20% casein diet. In addition, the soy protein diet decreased the incidence of glomerular sclerosis, and proinflammatory cytokines in kidney. Ingestion of the soy protein diet by control rats reduced the gene expression of SREBP-1, malic enzyme, FAS and increased HMG-CoAr, HMG-CoAs and LDLr. However, NS rats fed either casein or soy protein diets had low insulin concentrations with reductions in SREBP-1, FAS and malic enzyme expression compared with control rats fed the casein diet. NS rats fed the soy diet also had lower HMG-CoAr and LDLr mRNA levels than NS rats fed casein. In conclusion, the beneficial effects of soy protein on lipid metabolism are modulated in part by SREBP-1. However, in NS rats, the benefit may be through a direct effect of this protein on kidney rather than mediated by changes in expression of hepatic lipid metabolism genes.

Fasting insulin and uric acid levels but not indices of iron metabolism are independent predictors of non-alcoholic fatty liver disease. A case-control study

BACKGROUND

Non-alcoholic fatty liver disease is a common reason for hepatological consultation and may herald severe hepatic and extra-hepatic disease. The aetiopathogenesis of this condition is an area of increasing interest.

AIM

To evaluate anthropometric and biochemical factors associated to non-alcoholic fatty liver disease in a case-control study. Methods. Demographic and biochemical data of 60 consecutive patients with bright liver absent-to-low alcohol consumption, no evidence of viral, genetic and autoimmune diseases, were compared to those of 60 age- and gender-matched historical controls without fatty liver by univariate and multiple logistic regression analysis.

RESULTS

Patients were more often hypertriglyceridaemic, obese and diabetic than controls (p<.01). Mean values of alanine transaminase, gammaglutamyltranspeptidase, triglycerides, uric acid, fasting and log insulin, transferrin percent saturation and ferritin were significantly higher in the patients, while transferrin and quantitative insulin sensitivity check index, a quantitative insulin sensitivity index, were lower. No iron storage was found in those who underwent liver biopsy At univariate analysis the relative risk for non-alcoholic fatty liver disease significantly increased (p<0. 05) with increasing body mass index, fasting insulin, alanine transaminase, uric acid, triglycerides and gammaglutamyltranspeptidase; it decreased with increasing transferrin and quantitative insulin sensitivity check index. Multiple logistic regression analysis disclosed only fasting insulin and uric acid to be independent predictors of non-alcoholic fatty liver disease (p<0.05).

CONCLUSIONS

Fasting insulin and serum uric acid levels indicating insulin resistance, but not indices of iron overload, are independent predictors of non-alcoholic fatty liver disease.