Cross-over Pilot Study of Blood Cholesterol Response to Dietary Saturated Fat in Patients With Autosomal Dominant Hypercholesterolemia

Inclusion Criteria: 1. Adults, age \> 18 years or \< 80 years 2. Pre-treatment LDL-C greater than the 95th percentile for age and sex (corresponding to 190 mg/dL for most adults), with one of the 2 following criteria: (1) tendon xanthoma (proband or first-degree relative) or (2) either first-degree relative with premature CHD (age less than 55 years in men or 65 years in women) or pretreatment LDL-C greater than the 95th percentile for age and sex. 3. Willing to come off medical therapy 4 weeks before and during study. 4. Willing to follow high/low saturated fat diet 5. Willing to attend dietary counseling sessions 6. Willing to attend frequent clinic visits 7. Subjects willing to participate under the conditions described in the informed consent form (ICF) and able to sign the ICF and applicable HIPAA forms. Exclusion Criteria: 1. Presence of any clinically significant uncontrolled endocrine disease known to influence serum lipids or lipoproteins. Note: patients on thyroid replacement therapy can be included if the dosage of thyroxine has been stable for 6 weeks prior to the first study visit and thyroid-stimulating hormone (TSH) level is within the normal range. 2. Conditions of severe acute vascular stress (e.g. acute coronary syndrome, ischemic stroke, or major vascular surgery) within 3 months prior to the first study visit. 3. Patients unable to maintain their current activity level or planning to increase their activity level (e.g. new exercise regimen). 4. Pregnant or breast-feeding women. 5. Major illness 6. Secondary cause of dyslipidemia (e.g. obstructive liver disease, hypothyroidism, or nephrotic syndrome) 7. Hospitalization within 3 months 8. Substance abuse (illegal drug use, chronic alcoholism or problematic use of alcohol or total daily alcohol intake \>2 drinks per day in men and \> 1 drink per day in women). 9. Immunodeficiency or HIV-positive status 10. Illiteracy 11. Severe medical condition that may impair the ability of the person to participate in a nutrition intervention study (e.g. digestive disease with fat intolerance, advanced malignancy, or major neurological, psychiatric or endocrine disease) 12. Any other medical condition thought to limit survival to less than 1 year 13. Difficulties or major inconvenience to change dietary habits 14. History of food allergy with hypersensitivity to any of the components of olive oil or nuts