The Lean Living Study

Epidemiological studies have linked regular consumption of nuts with lower body mass index
and reduced likelihood of weight gain in adulthood. Several mechanisms have been proposed to
explain why nuts may facilitate weight management, including their high satiety property
which may promote dietary compensation with reduced subsequent energy intake. Although
proposed as a possible mediating factor, satiety and satiation in relation to nuts or
nut-containing meals have been examined in only a few previous studies. The effects of nut
consumption in the context of a weight loss intervention have been examined in only five
previously-published randomized studies, which have tested the effects of almonds, pistachios
or peanuts (but not walnuts) and have had mixed results.

This project is a study to investigate the effects of a walnut-enriched vs. standard
reduced-energy diet on body weight and satiety via pre- and post-meal ratings scales, as well
as exploring the response of satiety- and appetite-related gastrointestinal peptides to meals
with or without walnuts in a sample subset.

The specific aims of this study are:

1. To compare the effects of a walnut-enriched reduced-energy diet to a standard
reduced-energy diet on body weight and cardiovascular disease risk factors in a sample
of overweight and obese adults in an intensive 6-month weight loss intervention.

2. To examine whether there is a differential response in satiety- and appetite-related
ratings scales in association with a walnut-enriched reduced-energy diet and a standard
reduced-energy diet among the participants in this weight-loss study.

3. To examine the response of satiety- and appetite-related gastrointestinal peptides
(ghrelin, cholecystokinin, glucagon-like peptide, and peptide YY), to meals with or
without walnuts in a sample subset, as an exploratory aim.

The first two aims will be addressed in a randomized controlled study involving 100
overweight or obese men and women assigned to a walnut-enriched reduced-energy diet or a
standard reduced-energy diet in the context of a 6-month intensive weight loss intervention.
Subjective satiety- and appetite-related ratings will be collected at specific intervals
before lunch and dinner using visual analogue scales. Postprandial gastrointestinal peptide
response to a meal with or without walnuts, the third and exploratory aim, will be measured
in a subset of study participants (n=20) using a within-subject crossover study design.

The investigators hypothesize that participants assigned to the walnut-enriched diet study
arm will have greater weight loss and overall better improvements in cardiovascular disease
risk factors, and that ratings of hunger, fullness, and anticipated prospective consumption
will differ from those of participants assigned to the standard reduced-energy diet. The
investigators hypothesize that postprandial satiety- and appetite-related gastrointestinal
peptides, which play a role in short-term control of appetite and may be biomarkers of
satiety, may differ in response to different isocaloric meal composition. Results from this
study will contribute to understanding the role of nuts in weight control, including further
knowledge of the explanatory mechanisms, and will expand knowledge of how nuts in the diet
may contribute to the prevention and management of obesity.

Inclusion Criteria:

- aged 21 years and older

- BMI >27.0 kg/m2 and <40 kg/m2

- non-smoker

- willing and able to participate in clinic visits, group sessions, telephone, and
internet communications at specified intervals

- able to provide data through questionnaires and by telephone

- willing to maintain contact with the investigators for 6 months

- willing to allow blood collections

- no known allergy to tree nuts

- capable of performing a simple test for assessing cardiopulmonary fitness

Exclusion Criteria:

- inability to participate in physical activity because of severe disability

- a history or presence of a comorbid diseases for which diet modification and increased
physical activity may be contraindicated

- smoker

- self-reported pregnancy or breastfeeding or planning a pregnancy within the next year

- currently actively involved in another diet intervention study or organized weight
loss program

- a history or presence of a significant psychiatric disorder or any other condition
that, in the investigator's judgement, would interfere with participation in the trial