naturopathydigest.com -- Critical Research

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Critical Research

Critical Research is a regular feature in Naturopathy Digest. Each month, we provide abstracts from studies published in the top peer-reviewed journals; each abstract includes the complete citation and an online link to the journal. Whenever possible, this link directs you to a page where you can order the full text of the study, if desired.

This Month's Featured Abstract

Green tea consumption and cognitive function: a cross-sectional study from the Tsurugaya Project.

Shinichi Kuriyama, Atsushi Hozawa, Kaori Ohmori, et al.

Background: Background: Although considerable experimental and animal evidence show that green tea may possess potent activities of neuroprotection, neurorescue, and amyloid precursor protein processing that may lead to cognitive enhancement, no human data are available.
Objective: The objective of this study was to examine the association between green tea consumption and cognitive function in humans.
Design: We analyzed cross-sectional data from a community-based Comprehensive Geriatric Assessment (CGA) conducted in 2002. The subjects were 1,003 Japanese subjects age 70 or older. They completed a self-administered questionnaire that included questions about the frequency of green tea consumption. We evaluated cognitive function by using the Mini-Mental State Examination, with cutoffs of <28, <26, and <24, and calculated multivariate-adjusted odds ratios (ORs) of cognitive impairment.
Results: Higher consumption of green tea was associated with a lower prevalence of cognitive impairment. At the <26 cutoff, after adjustment for potential confounders, the ORs for the cognitive impairment asso-ciated with different frequencies of green tea consumption were 1.00 (reference) for 3 cups/wk, 0.62 (95% CI: 0.33, 1.19) for 4-6 cups/wk or 1 cup/d, and 0.46 (95% CI: 0.30, 0.72) for 2 cups/d (P for trend = 0.0006). Corresponding ORs were 1.00 (reference), 0.60 (95% CI: 0.35, 1.02), and 0.87 (95% CI: 0.55, 1.38) (P for trend = 0.33) for black or oolong tea and 1.00 (reference), 1.16 (95% CI: 0.78, 1.73), and 1.03 (95% CI: 0.59, 1.80) (P for trend = 0.70) for coffee. The results were essentially the same at cutoffs of <28 and <24.
Conclusion: A higher consumption of green tea is associated with a lower prevalence of cognitive impairment in humans.
Source: American Journal of Clinical Nutrition, February 2006; 83(2):355-361.

Calorie restriction induces mitochondrial biogenesis and bioenergetic efficiency.

G. López-Lluch, N. Hunt, B. Jones, et al.

Age-related accumulation of cellular damage and death has been linked to oxidative stress. Calorie restriction (CR) is the most robust, nongenetic intervention that increases lifespan and reduces the rate of aging in a variety of species. Mechanisms responsible for the anti-aging effects of CR remain uncertain, but reduction of oxidative stress within mitochondria remains a major focus of research. CR is hypothesized to decrease mitochondrial electron flow and proton leaks to attenuate damage caused by reactive oxygen species. We have focused our research on a related, but different, anti-aging mechanism of CR. Specifically, using both in vivo and in vitro analyses, we report that CR reduces oxidative stress at the same time that it stimulates the proliferation of mitochondria through a peroxisome proliferation-activated receptor coactivator 1a signaling pathway. Moreover, mitochondria under CR conditions show less oxygen consumption, reduce membrane potential, and generate less reactive oxygen species than controls, but remarkably, they are able to maintain their critical ATP production. In effect, CR can induce a peroxisome proliferation-activated receptor coactivator 1a-dependent increase in mitochondria capable of efficient and balanced bioenergetics to reduce oxidative stress and attenuate age-dependent endogenous oxidative damage.
Source: Proceedings of the National Academy of Sciences, Feb. 7, 2006;103(6):1768-73.

Predictors of worsening insulin sensitivity in postmenopausal women.

Gwen J. Goodrow, MD, Georgia D. L-Hommedieu, PA, Barbara Gannon, MD, and Cynthia K. Sites, MD

Objective: The purpose of this study was to determine predictors of worsening insulin sensitivity in postmenopausal women.
Study design: Seventy-one non-obese, postmenopausal women were assigned randomly to receive hormone replacement therapy (conjugated estrogens, 0.625 mg, plus medroxyprogesterone acetate, 2.5 mg) or placebo daily for one year (34 women received hormone replacement therapy, 37 women received placebo). At baseline and 12 months, the women received a computed tomography scan at the L4-L5 vertebral disk space, a dual X-ray absorptiometry scan, a euglycemic hyperinsulinemic clamp to measure insulin sensitivity, and a lipid profile. Declining insulin sensitivity was defined as the largest quartile change in insulin sensitivity in the women who received the placebo (–1.42 mg/min/kg lean body mass).
Results: By univariate analysis, we found that significant predictors of worsening insulin sensitivity were the use of hormone replacement therapy, baseline insulin sensitivity, a younger age, and <10 years since menopause. By logistic regression, we determined that hormone replacement therapy use and higher baseline insulin sensitivity were independent predictors of worsening insulin sensitivity.
Conclusion: The use of hormone replacement therapy and baseline insulin sensitivity are significant independent predictors of the development of worsening insulin sensitivity in postmenopausal women.
Source: American Journal of Obstetrics & Gynecology, February 2006;194(2):355-61.

The availability and cost of healthier food alternatives.

Karen M. Jetter, PhD, and Diana L. Cassady, DrPH

Background: Many people, especially low-income consumers, do not successfully follow dietary recommendations to eat more whole grains and less fat and added sugar. The food environment may have a significant impact on the choice by low-income consumers to eat healthier foods, as both the availability and price of healthier food items may limit their ability to maintain a healthier diet. We investigated the cost and availability of a standard market basket of foods, and a healthier basket that included low-fat meat and dairy and whole grain products.
Methods: Market-basket surveys were conducted in 25 stores in Los Angeles and Sacramento. Stores were selected from neighborhoods that were varied by income and surveyed three times from September 2003 to June 2004. The average cost of a standard market basket (based on the U.S. Department of Agriculture’s Thrifty Food Plan [TFP]) and a healthier market basket was calculated from these prices and compared using a standard t-test to determine if they were significantly different from each other. The analysis was conducted in 2005.
Results: In neighborhoods served by smaller grocery stores, access to whole-grain products, low-fat cheeses, and ground meat with <10% fat is limited. Among all items that were unavailable, 64% were in small grocery stores. For the 2-week shopping list, the average TFP market-basket cost was $194, and the healthier market-basket cost was $230. The average cost of the healthier market basket was more expensive by $36 due to higher costs of whole grains, lean ground beef, and skinless poultry. The higher cost of the healthier basket is equal to about 35% to 40% of low-income consumers’ food budgets of $2,410 a year.
Conclusions: The lack of availability in small grocery stores located in low-income neighborhoods, and the higher cost of the healthier market basket may be a deterrent to eating healthier among very low-income consumers. Public policies should take the food environment into account in order to develop successful strategies to encourage the consumption of healthier foods.
Source: American Journal of Preventive Medicine, January 2006;30(1):38-44.

Nutritional assessment and counseling for prevention and treatment of cardiovascular disease.

Barbara Olendski, MPH, Christopher Speed, MND, and Frank J. Domino, MD

Physicians face several barriers to counseling their patients about nutrition, including conflicting evidence of the benefit of counseling, limited training and understanding of the topic, and imperfect and varied guidelines to follow. Because cardiovascular disease remains the leading cause of death in industrialized nations, family physicians should provide more than pharmacologic interventions. They must identify the patient’s dietary habits and attitudes and provide appropriate counseling. Tools are available to help, and a seven-step approach to nutritional therapy for the dyslipidemic patient may be useful. These steps include recommending increased intake of plant proteins; increased intake of omega-3 fatty acids; modification of the types of oils used in food preparation; decreased intake of saturated and trans-fatty acids; increased intake of whole grains and dietary fiber (especially soluble fiber) and decreased intake of refined grains; modification of alcohol intake, if needed; and regular exercise. Recommendations should be accompanied by patient information handouts presenting acceptable substitutions for currently identified detrimental food choices.
Source: American Family Physician, Jan. 15, 2006;73:257-64, 265-8.

Effect of a high-protein breakfast on the postprandial ghrelin response.

Wendy AM Blom, Anne Lluch, Annette Stafleu, Sophie Vinoy, Jens J Holst, Gertjan Schaafsma and Henk FJ Hendriks

Background: The most satiating macronutrient appears to be dietary protein. Few studies have investigated the effects of dietary protein on ghrelin secretion in humans.
Objective: This study was designed to investigate whether a high-protein (HP) breakfast is more satiating than a high-carbohydrate breakfast (HC) through suppression of postprandial ghrelin concentrations or through other physiologic processes.
Design: Fifteen healthy men were studied in a single-blind, crossover design. Blood samples and subjective measures of satiety were assessed frequently for three hours after the consumption of two isocaloric breakfasts that differed in their protein and carbohydrate content (58.1% of energy from protein and 14.1% of energy from carbohydrate, compared with 19.3% of energy from protein and 47.3% of energy from carbohydrate). The gastric emptying rate was indirectly assessed with the acetaminophen absorption test.
Results: The HP breakfast de-creased postprandial ghrelin secretion more than did the HC breakfast (P < 0.01). Ghrelin concentrations were correlated with glucose-dependent insulinotropic polypeptide (r = –0.65; 95% CI: –0.85, –0.29) and glucagon concentrations (r = –0.47; 95% CI: –0.75, –0.03). Compared with the HC breakfast, the HP breakfast increased glucagon (P < 0.0001) and cholecystokinin (P < 0.01), tended to increase glucose-dependent insulinotropic polypeptide (P = 0.07) and glucagon-like peptide 1 (P = 0.10), and decreased the gastric emptying rate (P < 0.0001). Appetite ratings were not significantly different between the two treatments, and the HP breakfast did not significantly affect ad libitum energy intake.
Conclusions: The HP breakfast decreased postprandial ghrelin concentrations more strongly over time than did the HC breakfast. High associations between ghrelin and glucose-dependent insulinotropic polypeptide and glucagon suggest that stimulation of these peptides may mediate the postprandial ghrelin response. The HP breakfast also reduced gastric emptying, probably through increased secretion of cholecystokinin and glucagon-like peptide 1.
Source: American Journal of Clinical Nutrition, February 2006; 83(2):211-220.