Overview
Excess weight, nutrition, and blood sugar levels can all affect immune function, which in turn can affect participants risk for heart disease and type 2 diabetes (T2DM). It is not known how diet, blood sugar, and weight affect immune function.
The purpose of the study is to look at how weight, diet and high blood sugar levels affect immune function. Results of the study will be compared to results of the control group (which will go through the same activities as the experimental groups).
Description
Rationale: Obesity is associated with several risk factors (for example, high blood sugar, poor insulin response and inflammation) that increase risk of developing cardiovascular disease and type 2 diabetes (T2DM). Obesity is also associated with abnormalities in the immune system and an increased risk of infection. Specific components of the diet such, as high dietary intake of fat and sugar, influence not only the development of obesity but also the immune system. It is unknown if the immune abnormalities associated with obesity in humans are due to: 1) excess body fat and/or 2) elevated blood sugar levels, often seen in obesity and/or 3) overall diet quality of an individual (for example high fat and/or high sugar intakes).
Research aims: The overall aim of this research proposal is to determine if diet or alterations in blood sugar levels independently affect inflammation and immune function in obese subjects. To achieve this goal, three objectives will be pursued: 1) to determine how obesity affects inflammation and immune function; 2) to determine how alterations in blood sugar levels affect inflammation and immune function; 3) to identify specific dietary factors that affect changes in immune function that are related to obesity.
Methodology: The study will recruit 4 groups of subjects that are similar in age and sex: lean subjects with normal blood sugar levels (NG); obese subjects with normal blood sugar levels (obese-NG); obese subjects who are pre-diabetic (as defined by having high blood sugar levels - but not high enough to be defined as having diabetes; GI); obese subjects who have type 2 diabetes (obese-T2DM).
Participants will consume a typical North American/Canadian diet that will maintain their weight for a 4-week time period (all food will be provided for the subjects by the Human Nutrition Clinical Research Unit at the University of Alberta). Immune system markers (inflammation in the blood and the response of immune cells) and cardiovascular disease markers (blood sugar and insulin) will be compared among the 4 groups of participants before and at the end of the study.
A stool sample will also be collected before and after the diet intervention to look at the effects of weight and blood sugar levels on the type of bacteria in the participants gut as part of a Stool Sub-study. Research has shown that weight and blood sugar levels may affect the type of bacteria in the participants gut, which in turn can affect immune function and health risk. This is not a part of the main study, and the participants stool sample will be analyzed in future research.
Outcomes: By comparing these four groups, the investigators will be able to gain an understanding of the immune complications associated with obesity alone (ie excess body fat) and the relationship between blood sugar levels and diet with immune complications. Thus, this study will identify dietary interventions to counteract the immune abnormalities associated with obesity, which may in turn have implications for affecting the risk of cardiovascular disease and T2DM associated with obesity.
Eligibility
Inclusion Criteria:
- Men and women 18-65 years old that are lean (BMI < 25 kg/m2) and obese (BMI > 30 kg/m2) will be recruited in the Edmonton area.
- Waist circumference (cm) criteria: A waist circumference of 102 cm or more in men, or 88cm in women, is associated with health problems such as type 2 diabetes.
- Fasting blood glucose levels: lean-NG and obese-NG will have values less than 5.6 mmol/L, Obese-GI will have levels greater than 5.6 mmol/L, but less than 7 mmol/L; and obese-T2DM will have levels greater than or equal to 7 mmol/L.
- HbA1c levels: lean-NG and obese-NG will have levels less than 5.6%; obese-GI will have levels greater than 5.6% but less than 6.5%; obese-T2DM will have levels greater than or equal to 6.5%, but less than 10%.
- Blood Pressure criteria: lean-NG and obese-NG as being healthy, a blood pressure criterion of less than 130/85 mmHg will be required (represents systolic pressure/diastolic pressure).
- Triglycerides (TGs) and high density lipoprotein cholesterol (HDL-C): Lean-NG and obese-NG subjects will have TG levels less than 1.7 mmol/L, and HDL-C levels greater than 1.03 mmol/L for men and greater than 1.29 mmol/L for women.
Exclusion Criteria:
- Health status: individuals with a previous history of cardiovascular disease, renal disorder, monogenic dyslipidemia, presence of an endocrine disorder other than T2DM
- Diabetes: newly diagnosed individuals (< 6 months) or those with poorly controlled (HbA1C > 8.0%) diabetes
- Pregnant or lactating women:
- individuals taking chronic anti-inflammatory drugs or supplements (including aspirin, antihistamines and omega-3 supplements)
- Smokers:
- men and women whose body weight has not been stable for at least 6 months prior to the study
- Participants who cannot comply to greater than or equal to 90% of the feeding protocol
- If a potential participant has many food allergies, where the allergic reaction is potentially life threatening
- Pacemaker or internal electrical device