Effects of Walnuts on Central Blood Pressure, Arterial Stiffness Indices, Lipoproteins, and Other CVD Risk Factors

Diets containing nuts likely reduce cardiovascular disease (CVD) risk but the mechanisms
remain poorly defined. Walnuts contain substantial amounts of polyunsaturated fatty acids
(PUFAs), particularly alpha-linolenic acid (ALA), and are a rich source of bioactives. Many
vegetable oils are high in PUFAs but most lack ALA and do not provide the same complement of
bioactive compounds as walnuts. ALA is thought to improve cardiovascular health by modulating
circulating lipid concentrations, altering membrane structure/function by enhancing the total
ω-3 fatty acid content of cell membrane phospholipids, and reducing inflammatory reactions by
inhibiting production of arachidonic acid-derived eicosanoids. Consumption of walnuts has
consistently been shown to improve blood lipids/lipoproteins and vascular health. However,
there remains much debate over what is the preferable replacement for saturated fat in the
diet. Because of the ALA and bioactives that they provide, walnuts may confer specific CVD
benefits. To study the effects of walnuts, in terms of both their ALA content and bioactive
compounds, we will compare two test diets (one containing walnuts and one matched for PUFA
and ALA content but devoid of walnuts and their bioactives) to a control diet matched for
macronutrient and linoleic acid (LA) content but providing oleic acid in place of ALA. This
diet design will provide information about how walnuts affect the selected endpoints of
interest due to their bioactives as well as their ALA content, and whether walnut ALA is a
superior substitute for dietary saturated fat compared to oleic acid.

Feeding protocol and study treatments:

This study is designed as a double-blind, 3-period, randomized, cross-over controlled feeding
study. Prior to randomization, participants will complete a two week run-in on a standard
Western diet. Each diet period treatment phase will be 6 weeks in duration, separated by
2-week washout periods. The three test diets are: 1) a walnut diet (WD; providing ~2.0 oz of
walnuts per day); 2) a matched walnut control diet (WCD) that will provide the same fatty
acid profile as the walnut diet, but will not contain walnuts (and their bioactives); and 3)
a low ALA diet (LAD) with a similar macronutrient (and linoleic acid) composition as the WD
and WCD, but using oleic acid to replace ALA. Study diets will be prepared in a metabolic
kitchen, with three isocaloric meals and a snack provided each day, based on a 7-day rotating
menu cycle. Participants will be instructed to consume only the prepared foods and limit
their intake of alcohol to 2 drinks/week and caffeinated calorie-free beverages to 40 ounces
(5 drinks) per day. Diets will be planned for every subject according to his/her energy
requirements and will be nutritionally adequate. This diet design will permit the WD to be
compared with the WCD and LAD and, thereby, allow us to ascertain the specific effects that
walnuts and their bioactive components (including and beyond ALA) may have on CVD risk
factors and artery health.

Inclusion Criteria:

- Aged 30-65 years

- BMI greater than 25 and less than or equal to 40 kg/m2

- Non-smokers

- TG < 350 mg/dL

- LDL-C between the 25-95th percentile from NHANES:

- Males: 105-194 mg/dL

- Females: 98-190 mg/dL

- Stage I hypertension:

- SBP > 120 mmHg and/or DBP > 80 mmHg

- SBP < 160 mmHg and DBP < 100 mmHg

- Free of established CVD, stroke, diabetes, liver, kidney or autoimmune disease.

Exclusion Criteria:

- Elevated BP (SBP ≥160 mmHg OR DBP ≥ 100 mmHg)

- A history of myocardial infarction, stroke, diabetes mellitus, liver disease,
inflammatory disease, kidney disease, and/or thyroid disease (unless controlled on
medication).

- Blood pressure or cholesterol-lowering medication use

- Refusal to discontinue intake of putative cholesterol-lowering supplements (psyllium,
fish oil capsules, soy lecithin, niacin, fiber, flax, and phytoestrogens).

- Vegetarianism or other dietary practices that are inconsistent with the test diets

- Nut allergies (Other food allergies will be reviewed on a case-by-case basis)

- Refusal to discontinue nutritional supplements, herbs, vitamins or NSAID's

- Latex allergy

- Pregnant or lactating females