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The Effects of Regular Nut Consumption on Cardiovascular Health
24 September 2007
In recent years, there have been countless articles in written media and segments on television news programs about the search for a nutritional "magic bullet": a food that has the ability to ward off cancer, reverse the signs of aging, and unclog arteries, all by just consuming a handful or two a day while still eating the same greasy, trans fat laden food as before. Many of the candidates submitted for this coveted dietary position include foods such as flaxseed, orange juice, and blueberries. It is not surprising that foods like these would be on such a list, since for most people fruits and healthy grains have been a highly recommended part of the diet ever since early childhood. Nevertheless, there is one food that magazines and television shows have hailed as a panacea for heart disease and a preventive measure for cancer that previously has only been a food for parties and bars: nuts. In Reader's Digest, articles have claimed that nuts can lower blood sugar, raise the level of HDL ("good") cholesterol, and aid in weight loss (http://www.rd.com/content/nuttin-wrong-with-nuts/). Snack food companies, such as Planters and Diamond have even published web pages and brochures extolling the virtues of indulging in their products on regular basis, capitalizing as much as possible on the positive media buzz (http://www.nutnutrition.com/articles/nuts_are_nutrient_dense.html, http://www.diamondnuts.com/docs/nutsforhealthyliving.pdf). All of these publications cite unspecified "studies" and invoke the name of the respectable USDA, creator of that monolith of nutrition, the food pyramid, to lend credibility to their amazing claims. Before supplementing one's diet in any nontraditional way, however, a health conscious individual should investigate the medical literature to determine if the claims to nuts' ability to lower the risk for heart disease are true or simply the latest marketing scheme.
Because many risk factors for diabetes are also risk factors for heart disease (a low HDL cholesterol level (<35), high triglyceride levels (>250 mg/dL), and excess weight (especially around the waist)), and diabetes can result in hypertension, prevention of diabetes is very closely related to the prevention of heart disease (http://www.nlm.nih.gov/medlineplus/ency/article/002072.htm#Information). According to 2005 data from the National Diabetes Information Clearinghouse, 20.8 million Americans are currently living with either Type I or Type II diabetes, with an incidence of 1.5 million in that year. The healthcare for these millions of individuals is estimated to be approximately $132 billion a year in diabetes management, treatment for complications, work loss, and premature mortality. (http://diabetes.niddk.nih.gov/dm/pubs/statistics/index.htm#14)
Since there is currently no cure for this debilitating condition, prevention is key to reduce the prevalence of the disease and its drain on the economy. Since these factors, along with hypertension resulting from diabetes, are also risk factors for heart disease, the prevention of diabetes is highly related to maintenance of cardiovascular health.
One of the most visible care requirements for diabetes is blood sugar monitoring and control. Diabetes in general is a condition in which the patient's body either severely underproduces insulin or is insulin resistant, so blood sugar can easily rise to unsafe levels after eating and lead to a host of problems over time. In a study by L.S. Augustin, et al. at St. Michael's Hospital in Toronto, Ontario, the effects of a post meal serving of almonds on postprandial glycemia were studied. Nine healthy individuals (mean age= 27.8) of average body mass index (BMIaverage=22.9 kg/m2) were fed five total meals consisting of white bread after a 10 to 12 hour overnight fast, with each meal separated by at least one day. Two control meals of white bread only were served, one as the first meal and the other as the last meal of the study, with three test meals served in between that included 30, 60, or 90 g of almonds in addition to the bread. After consumption, the subjects' blood sugar was measured by a conventional pinprick capillary method seven times over the next two hours, and a two hour glucose curve plotted (Figure 1). The results showed a significant reduction in the post meal glucose levels of the subjects with each successive increase in the almond supplement. When a subject consumed 90 g of almonds with the meal, his or her blood glucose experienced an average postprandial blood glucose level increase of only about 1.5 mM, versus an increase of about 2.5 mM for the control meal. It is hypothesized that the effect of the almonds on blood glucose levels is a result of many factors. Almonds are a good source of both protein and fat, which inhibit gastric emptying and thus slow the passage of the bolus into the duodenum where most absorption occurs. In addition, the unblanched almonds used in the study are rich in chemicals called phenolics and phylates that are amylase inhibitors. Decreased amylase activity means a lower rate of carbohydrate digestion and thus a less drastic glycemic response. Though a study with a larger sample should be undertaken, these results suggest that almonds (or any nut) can be effective tools for controlling glycemia. (Augustin)
While maintenance of healthy blood glucose levels is important to cardiovascular health secondhand through diabetes, correction of unhealthy blood lipid profiles is directly related to a decreased incidence of heart disease. A person's risk for heart disease increases significantly under any or all of the following lipid conditions:
total cholesterol: >239 mg/dL
triglycerides: >199 mg/dL
LDL ("bad") cholesterol: >159 mg/dL
HDL cholesterol: <40 mg/dL
The results of a study conducted by E. Akgül, et al. at Hacettepe University in Ankara, Turkey, showed that dietary supplementation with hazelnuts improves the levels of triglycerides, HDL cholesterol, and some lipoproteins significantly, while showing a statistically insignificant yet decreasing trend for LDL and total cholesterol in fifteen hypercholesterolemic men. The study used a two phase design, consisting of first phase (P1) of four weeks in which a control diet that was low in cholesterol, low in fat, and high in carbohydrates was given, and a second phase (P2) also of four weeks in which the control diet was supplemented with 40 g/day of hazelnuts. Lipid profiles were taken throughout. After P2, the subjects showed an average decrease of 31.8% in triglyceride levels and a 12.6% increase in HDL cholesterol concentration while showing a 5.2% decrease in total cholesterol levels and a 3.3% decrease in LDL cholesterol concentration. (Akgül) These findings were further bolstered by a study conducted by R.U. Almario, et al. at the University of California, Davis. This study not only corroborated the findings of the Akgül study but also showed that despite the increased caloric intake as a result of the high fat level of the walnut supplementation used body weight did not increase. (Almario) A finding such as this helps to silence a major criticism of nut supplementation: while subclasses of the lipid profile may improve, there will be a net decrease in cardiovascular health as a result of the increased fat intake from the nuts. A similar study found the same was true for pecans in people with normal lipid profiles as well (Clayshulte).
These salutatory cardiovascular effects are attributable to the high content of beneficial lipids in nuts. A study at Northwestern University in 1990 attributed to increases in cholesterol to significant consumption of dietary cholesterol and saturated fat and decreases in total cholesterol to dietary fiber and monounsaturated and polyunsaturated fats, specifically highlighting the qualities of omega-3 fatty acids that seemed to have the ability to not only have the ability to lower triglyceride levels but also decrease the incidence of thrombosis, which may lead to myocardial infarction (Stone). Each of these beneficial nutrients is present in significant levels in many nuts without significant levels of the previously mentioned undesirable nutrients. Nearly 60 percent of the fat in pecans is monounsaturated, with 30% of the remainder being polyunsaturated (http://www.ilovepecans.org/nutrition.html#heart). Walnuts contain not only high levels of monounsaturated and polyunsaturated fats, but also contain significant concentrations of omega-3 and omega-6 fatty acids (http://www.walnutinfo.com/health.html). In addition to the beneficial fats, walnuts also contain tocopherol (vitamin E) in appreciable levels (Galvin), which has been shown to aid heart health in many ways, including improving the cholesterol profile (Faucett).
From the findings of the research studies examined, it appears that the claims of countless media outlets and nut producers are true. Investigation has shown that all types of nuts over salutatory effects for cardiovascular health. By regulating the postprandial blood glucose level, almonds can help prevent the onset of diabetes or help keep it under control, thus avoiding a common cause of hypertension (Augustin). This attribute can be extended to other nuts as well, since they all contain high levels of protein and fat. Specific nutrients in nuts, such as monounsaturated and polyunsaturated fats, tocopherol, and omega fatty acids help control a patient's lipid profile, keeping levels of triglycerides, total cholesterol, and LDL cholesterol low while raising the level of HDL cholesterol (Akgül, Almario, Clayshulte, Faucett). Since nut supplementation seems to have no ill effects in moderation (absent of any allergies), it appears highly advisable that a person should try to consume a modest amount of nuts regularly for cardiovascular health, especially if he or she is at risk for or has heart disease.
plasma cholesterol and lipoprotein levels in hypercholesterolemic adult men.
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walnut consumption on plasma fatty acids and lipoproteins in combined
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Fatty acid profile, tocopherol, squalene, and phylosterol content of walnuts,
almonds, peanuts, hazelnuts, and the macadamia nut. Int J Food Sci Nutr, 55(3), 171—178.
North Am, 19(2), 321-344.
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