A systematic review of the effects of nuts on blood lipid profiles in humans

Effect of almond-enriched high-monounsaturated fat diet on selected markers of inflammation: a randomised, controlled, crossover study

Frequent consumption of nuts lowers the risk of CHD. While lowering blood lipids is one of the mechanisms for cardioprotection, the present study sought to determine whether monounsaturated fat-rich almonds also influence other CHD risk factors such as inflammation and haemostasis. This was a randomised, controlled, crossover feeding study with twenty-five healthy adults (eleven men; fourteen women), age 22-53 years. Following a 2 week run-in phase (34 % energy from fat), subjects were assigned in random order to three diets for 4 weeks each: a heart-healthy control diet with no nuts ( < 30 % energy from fat), low-almond diet and high-almond diet (10 % or 20 % isoenergetic replacement of control diet with almonds, respectively). Serum E-selectin was significantly lower on the high-almond diet compared with the control diet. E-selectin decreased as the percentage of energy from almonds increased (P < 0.0001). C-reactive protein (CRP) was lower in both the almond diets compared with the control diet. A clear dose response was not observed for either E-selectin or CRP. There was no effect of diet on IL-6 or fibrinogen. Tissue plasminogen activator antigen was significantly lower on the control and high-almond diets compared with the low-almond diet, although the values were within normal range. In conclusion, consumption of almonds influenced a few but not all of the markers of inflammation and haemostasis. A clear dose response was not observed for any of the markers studied.

Nut consumption and risk of type II diabetes in the Physicians' Health Study

BACKGROUND/OBJECTIVES

While type II diabetes (DM) is a major cause of morbidity in the United States, limited data are available on the association between nut intake and incident DM. We sought to examine the association between nut consumption and the risk of DM.

SUBJECTS/METHODS

Prospective cohort of 20 224 male participants of the Physicians' Health Study I. Nut consumption was estimated using a 19-item brief food frequency questionnaire, and incident DM was ascertained through yearly follow-up questionnaires. Cox regression was used to estimate relative risks of DM.

RESULTS

The average age of the study participants was 54.4+/-9.4 years (range: 40.7-87.1). During a mean follow-up of 19.2 years, 1828 cases of DM occurred. The crude incidence rates of DM were 4.82, 4.85, 4.92, 4.16, 4.29 and 3.32 cases per 1000 person-years for individuals reporting nut consumption of rarely/never, <1, 1, 2-4, 5-6 and 7+ servings per week, respectively. While nut consumption was associated with a lower risk of DM in a model adjusted for age (P for tend 0.017), such relation was attenuated on additional control for other confounders (multivariable adjusted hazard ratios (95% confidence interval) for DM were 1.0 (reference), 1.06 (0.93-1.20), 1.10 (0.95-1.26), 0.97 (0.82-1.14), 0.99 (0.76-1.30) and 0.87 (0.61-1.24) from the lowest to the highest category of nut consumption, respectively (P for trend 0.99). No statistically significant association between nut consumption and DM was found in either lean or overweight/obese participants.

CONCLUSIONS

Our data do not show an association between nut consumption and incident DM in US male physicians.

Position of the American Dietetic Association: vegetarian diets

It is the position of the American Dietetic Association that appropriately planned vegetarian diets, including total vegetarian or vegan diets, are healthful, nutritionally adequate, and may provide health benefits in the prevention and treatment of certain diseases. Well-planned vegetarian diets are appropriate for individuals during all stages of the life cycle, including pregnancy, lactation, infancy, childhood, and adolescence, and for athletes. A vegetarian diet is defined as one that does not include meat (including fowl) or seafood, or products containing those foods. This article reviews the current data related to key nutrients for vegetarians including protein, n-3 fatty acids, iron, zinc, iodine, calcium, and vitamins D and B-12. A vegetarian diet can meet current recommendations for all of these nutrients. In some cases, supplements or fortified foods can provide useful amounts of important nutrients. An evidence- based review showed that vegetarian diets can be nutritionally adequate in pregnancy and result in positive maternal and infant health outcomes. The results of an evidence-based review showed that a vegetarian diet is associated with a lower risk of death from ischemic heart disease. Vegetarians also appear to have lower low-density lipoprotein cholesterol levels, lower blood pressure, and lower rates of hypertension and type 2 diabetes than nonvegetarians. Furthermore, vegetarians tend to have a lower body mass index and lower overall cancer rates. Features of a vegetarian diet that may reduce risk of chronic disease include lower intakes of saturated fat and cholesterol and higher intakes of fruits, vegetables, whole grains, nuts, soy products, fiber, and phytochemicals. The variability of dietary practices among vegetarians makes individual assessment of dietary adequacy essential. In addition to assessing dietary adequacy, food and nutrition professionals can also play key roles in educating vegetarians about sources of specific nutrients, food purchase and preparation, and dietary modifications to meet their needs.

Nuts and health outcomes: new epidemiologic evidence

This article reviews recent epidemiologic evidence on nut intake and health outcomes. It focuses on studies in which nut consumption is directly assessed or when nuts are included in a dietary score or pattern. Epidemiologic studies have been remarkably consistent in showing an association between nut consumption and a reduced risk of coronary heart disease (CHD). Some evidence has emerged recently to suggest health-protective benefits of nuts other than CHD. Frequent nut intake probably reduces risk of diabetes mellitus among women, but its effects on men are unknown. Evidence on the anticarcinogenic effects of nuts is somewhat limited because studies in the past 2 decades have examined only 3 tumor sites, and the benefits appear to be manifested only in women. However, the protective benefits of frequent nut consumption on gallstone diseases are observed in both sexes. Long-term nut consumption is linked with lower body weight and lower risk of obesity and weight gain. A dietary pattern or score that includes nuts is consistently related with beneficial health outcomes, and this provides an indirect evidence of the salutary benefits of nut consumption. More longitudinal studies are needed to clarify the possible effects of nuts on diseases other than CHD.

Nuts and novel biomarkers of cardiovascular disease

Nuts are energy-dense foods, rich in total fat and unsaturated fatty acids. The favorable fatty acid profile probably contributes to the beneficial effects of nut consumption observed in epidemiologic studies (prevention of coronary heart disease and diabetes) and feeding trials (cholesterol lowering). Besides fat, the complex matrices of nuts contain many bioactive compounds: vegetable protein, fiber, minerals, tocopherols, and phenolic compounds. By virtue of their unique composition, nuts are likely to benefit newer cardiovascular risk biomarkers, such as LDL oxidizability, soluble inflammatory molecules, and endothelial dysfunction. Protection of LDL oxidation by nut intake has been documented in some, but not all, clinical studies. In one study, feeding one daily serving of mixed nuts was associated with lower oxidized LDL concentrations. Regarding inflammation, cross-sectional studies have shown that nut consumption is associated with lower concentrations of circulating inflammatory molecules and higher plasma adiponectin, a potent antiinflammatory adipokine. Clinical studies with nuts have documented reduced inflammatory cytokine concentrations but no consistent changes of C-reactive protein. Only walnuts have been formally tested for effects on endothelial function. After both walnut diets and single walnut meals, favorable vasoreactivity changes have been observed. Walnut consumption also reduced expression of endothelin 1, a potent endothelial activator, in an animal model of accelerated atherosclerosis. Beneficial effects on vascular reactivity may be ascribed to several constituents of walnuts: l-arginine, the precursor of nitric oxide, alpha-linolenic acid, and phenolic antioxidants. Although more studies are warranted, the emerging picture is that nut consumption beneficially influences cardiovascular risk beyond cholesterol lowering.

Effect of polyphenol-rich extract from walnut on diet-induced hypertriglyceridemia in mice via enhancement of fatty acid oxidation in the liver

The kernel pellicles of walnut are rich in ellagitannins with antioxidative activity. A polyphenol-rich extract from walnuts (WP, 45% polyphenol) was prepared and evaluated for its hypolipidemic effect in high fat diet fed mice. Oral administration of WP (100 and 200 mg/kg) significantly reduced liver weight and liver and serum triglycerides (TG). Hepatic beta-oxidation in cytosol, including peroxisome, was enhanced by WP (50-200 mg/kg). mRNA expressions of hepatic peroxisome proliferator-activated receptor (PPAR) alpha and acyl coenzyme A oxidase (ACOX) 1 were enhanced by WP (50-200 mg/kg). With respect to the hypotriglyceridemic mechanism of WP, it suppressed neither olive oil induced serum TG elevation in mice nor oleic acid induced TG accumulation in HepG2 cells. On the other hand, mRNA expressions of PPARalpha, ACOX1, and carnitine palmitoyltransferase (CPT) 1A in HepG2 cells were significantly enhanced by addition of WP (100 microg/mL). Moreover, tellimagrandin I, a polyphenolic constituent in WP, enhanced ACOX1 expression at 1-100 microg/mL. In conclusion, WP was found to possess hypotriglyceridemic activity via enhancement of peroxisomal fatty acid beta-oxidation in the liver. These results suggest that tellimagrandin I is involved in the hypotriglyceridemic mechanism of WP.

Walnut polyphenols prevent liver damage induced by carbon tetrachloride and d-galactosamine: hepatoprotective hydrolyzable tannins in the kernel pellicles of walnut

The polyphenol-rich fraction (WP, 45% polyphenol) prepared from the kernel pellicles of walnuts was assessed for its hepatoprotective effect in mice. A single oral administration of WP (200 mg/kg) significantly suppressed serum glutamic oxaloacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT) elevation in liver injury induced by carbon tetrachloride (CCl 4), while it did not suppress d-galactosamine (GalN)-induced liver injury. In order to identify the active principles in WP, we examined individual constituents for the protective effect on cell damage induced by CCl 4 and d-GalN in primary cultured rat hepatocytes. WP was effective against both CCl 4- and d-GalN-induced hepatocyte damages. Among the constituents, only ellagitannins with a galloylated glucopyranose core, such as tellimagrandins I, II, and rugosin C, suppressed CCl 4-induced hepatocyte damage significantly. Most of the ellagitannins including tellimagrandin I and 2,3- O-hexahydroxydiphenoylglucose exhibited remarkable inhibitory effect against d-GalN-induced damage. Telliamgrandin I especially completely suppressed both CCl 4- and d-GalN-induced cell damage, and thus is likely the principal constituent for the hepatoprotective effect of WP.

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.

[Vegetarian nutrition: Preventive potential and possible risks. Part 1: Plant foods]

Today vegetarian nutrition is more accepted and widespread in Europe than in former years. For a long time scientific research on vegetarian diets has focused mostly on malnutrition, whereas nowadays research centers increasingly on the preventive potential of plant-based diets. We followed a nutritive and a metabolic-epidemiological approach to obtain dietary recommendations. A MEDLINE research was performed for all plant food groups relevant for a vegetarian diet (key words: all relevant food groups, "vegetarian diet", "chronic disease", "cancer", "cardiovascular disease", "diabetes mellitus", "osteoporosis"). All relevant food groups were characterized regarding their nutrient content and rated with respect to the available metabolic-epidemiological evidence. Based on the evidence criteria of the WHO/FAO, cancer risk reduction by a high intake of vegetables and fruits is assessed as probable or possible, while a lowered risk of cardiovascular disease is convincing and a lowered risk of osteoporosis is probable. The evidence of a risk reducing effect of whole grain relating to colorectal cancer is assessed as possible, whereas it is probable relating to cardiovascular disease and diabetes mellitus type 2. There is an insufficient risk-reducing effect of legumes like soja relating to epithelial tumours and cardiovascular disease. The evidence of a risk-reducing effect of nuts to cardiovascular disease is assessed as probable, and in relation to cholelithiasis and diabetes mellitus type 2 as possible and insufficient, respectively. In conclusion, high consumption of fruits, vegetables, whole grains and nuts can lower the risk for several chronic diseases.

Fatty acid composition of nuts--implications for cardiovascular health

It is well established that, due to their high content of saturated fatty acids (SFA), the intake of meat and meat products is strongly associated with elevated blood cholesterol concentrations and an increased risk of hypertension, diabetes and cardiovascular diseases. Conversely, the intake of foods rich in unsaturated fatty acids, such as those contained in most vegetable fats and oils and oily fish, is associated with improved lipid profiles, a lower potency of intermediate biomarkers of atherosclerosis and lesser incidence of cardiovascular diseases. There are persuasive evidences that dietary substitution of monounsaturated fatty acids (MUFA) or n-6 polyunsaturated fatty acids (PUFA) for SFA lowers blood cholesterol and may have beneficial effects on inflammation, thrombosis, and vascular reactivity. MUFA may have an advantage over PUFA because enrichment of lipoprotein lipids with MUFA increases their resistance to oxidation. Marine n-3 PUFA have a number of anti-atherosclerotic effects, including anti-arrhythmic properties and, at relatively high doses, reduce serum triglycerides. These effects appear to be shared in part by vegetable n-3 PUFA. Nuts are natural foods rich in unsaturated fatty acids; most nuts contain substantial amounts of MUFA, while walnuts are especially rich in both n-6 and n-3 PUFA. Healthy fats in nuts contribute to the beneficial effects of frequent nut intake observed in epidemiological studies (prevention of coronary heart disease, diabetes, and sudden death) and in short-term feeding trials (cholesterol lowering, LDL resistance to oxidation, and improved endothelial function).

Health benefits of nuts: potential role of antioxidants

A diet rich in fruits, vegetables and minimally refined cereals is associated with lower risk for chronic degenerative diseases. Since oxidative stress is common in chronic degenerative disease, it has been assumed that dietary antioxidants may explain this protective effect. Every dietary plant contains numerous types of antioxidants with different properties. Many of these antioxidants cooperate in oxidative stress reduction in plants, and we hypothesize that many different antioxidants may also be needed for the proper protection of animal cells. To test this hypothesis, it is useful to identify dietary plants with high total antioxidant content. Several nuts are among the dietary plants with the highest content of total antioxidants. Of the tree nuts, walnuts, pecans and chestnuts have the highest contents of antioxidants. Walnuts contain more than 20 mmol antioxidants per 100 g, mostly in the walnut pellicles. Peanuts (a legume) also contribute significantly to dietary intake of antioxidants. These data are in accordance with our present extended analysis of an earlier report on nut intake and death attributed to various diseases in the Iowa Women's Health Study. We observed that the hazard ratio for total death rates showed a U-shaped association with nut/peanut butter consumption. Hazard ratio was 0.89 (CI = 0.81-0.97) and 0.81 (CI = 0.75-0.88) for nut/peanut butter intake once per week and 1-4 times per week, respectively. Death attributed to cardiovascular and coronary heart diseases showed strong and consistent reductions with increasing nut/peanut butter consumption. Further studies are needed to clarify whether antioxidants contribute to this apparent beneficial health effect of nuts.

Dietary fibre, nuts and cardiovascular diseases

Dietary fibre has a range of metabolic health benefits. Through a variety of mechanisms, dietary fibre, and the viscous variety in particular, slows down gastric emptying and intestinal transit, decreases the rate of intestinal carbohydrate absorption, and increases faecal bile acid excretion. Therefore, consumption of some types of soluble fibre can enhance satiety, which is associated with a lower BMI, and reduce blood cholesterol and the postprandial glucose response. Surprisingly, the consumption of insoluble fibre from whole grains, though metabolically inert, has been associated with a reduction in the risk of developing coronary heart disease and diabetes in epidemiological studies. The likely reason is that whole grains, like nuts, legumes and other edible seeds, contain many bioactive phytochemicals and various antioxidants. After cereals, nuts are the vegetable foods that are richest in fibre, which may partly explain their benefit on the lipid profile and cardiovascular health.

Effects of a high walnut and high cashew nut diet on selected markers of the metabolic syndrome: a controlled feeding trial

We investigated the effects of a high walnut diet and a high unsalted cashew nut diet on selected markers of the metabolic syndrome. In a randomized, parallel, controlled study design, sixty-four subjects having the metabolic syndrome (twenty-nine men, thirty-five women) with a mean age of 45 (sd 10) years and who met the selection criteria were all fed a 3-week run-in control diet. Hereafter, participants were grouped according to gender and age and then randomized into three groups receiving a controlled feeding diet including walnuts, or unsalted cashew nuts or no nuts for 8 weeks. Subjects were required to have lunch at the metabolic ward of the Nutrition Department of the North-West University (Potchefstroom Campus). Both the walnut and the unsalted cashew nut intervention diets had no significant effect on the HDL-cholesterol, TAG, total cholesterol, LDL-cholesterol, serum fructosamine, serum high-sensitivity C-reactive protein, blood pressure and serum uric acid concentrations when compared to the control diet. Low baseline LDL-cholesterol concentrations in the cashew nut group may have masked a possible nut-related benefit. Plasma glucose concentrations increased significantly (P = 0·04) in the cashew nut group compared to the control group. By contrast, serum fructosamine was unchanged in the cashew nut group while the control group had significantly increased (P = 0·04) concentrations of this short-term marker of glycaemic control. Subjects displayed no improvement in the markers of the metabolic syndrome after following a walnut diet or a cashew nut diet compared to a control diet while maintaining body weight.

Tree nuts and the lipid profile: a review of clinical studies

Tree nuts have a fatty acid profile that favourably affects blood lipids and lipoproteins. They are low in saturated fat and high in unsaturated fatty acids and are rich sources of other nutrients. An extensive database consistently shows total and LDL cholesterol-lowering effects of diets low in saturated fat and cholesterol and high in unsaturated fat provided by a variety of tree nuts. Collectively, a summary of studies conducted to date shows that tree nuts reduce LDL cholesterol by 3–19 % compared with Western and lower-fat diets. Nuts also contain many nutrients and bioactive compounds that appear to contribute to the favourable effects on lipids and lipoproteins – these include plant sterols, dietary fibre and antioxidants. Because of their unique nutrient profile, nuts can be part of a diet that features multiple heart-healthy foods resulting in a cholesterol lowering response that surpasses that of cholesterol-lowering diets typically used to reduce CVD risk.

Edible nuts and metabolic health

PURPOSE OF REVIEW

This review summarizes evidence for metabolic health benefits of tree nuts and groundnuts (peanuts). While a role for nuts in the dietary management of LDL-cholesterol is well established, it is evident that regular consumption of nuts may also help to counteract other cardiovascular and metabolic risk factors.

RECENT FINDINGS

Nuts are not only energy dense foods, they are rich sources of monounsaturated and polyunsaturated fatty acids and other bioactive nutrients with important metabolic effects. Contrary to expectations, epidemiological studies indicate that regular consumption of nuts is unlikely to contribute to obesity or increased risk of diabetes. In fact, it may help to regulate body weight by suppressing appetite and fat absorption. Nut consumption counteracts dyslipidemia and has the capacity to improve circulatory function through the actions of multiple constituents (arginine, polyphenols) on endothelial mechanisms.

SUMMARY

Nuts are densely packaged nutrients with wide-ranging cardiovascular and metabolic benefits, which can be readily incorporated in healthy diets. Their potential role in counteracting obesity and the metabolic syndrome warrants further investigation.