Clinical techniques

Members of the Metabolic Basis of Human Adipose Tissue in Health and Disease Research Laboratory are experts in a number of unique and specialized clinical techniques. We welcome questions about collaboration and training opportunities from research teams at Mayo Clinic and from other institutions.

Adipose tissue microdialysis

This in vivo technique involves insertion of a microdialysis probe into subcutaneous adipose tissue to continuously sample interstitial fluid. This technique allows researchers to measure local metabolites — for example, glycerol, glucose or lactate — to assess adipose tissue lipolysis and metabolic activity under physiological conditions.

Body composition

Calculation of body composition includes:

• Taking whole-body and regional fat mass, lean mass and bone mineral density measurements using dual-energy X-ray absorptiometry (DXA or DEXA).
• Estimating visceral adipose tissue by integrating DXA-derived body composition data with single-slice computerized tomography (CT) imaging at the L2-L3 vertebral level.
• Quantifying intramuscular adipose tissue in the thigh using CT imaging combined with advanced AI-assisted contouring techniques to enable precise delineation of muscle and fat compartments.

Diet manipulation

Researchers implement controlled dietary interventions varying caloric intake, macronutrient composition or the timing of meals. We use diet manipulation to investigate metabolic regulation, substrate utilization and adaptive responses to nutritional challenges under tightly monitored conditions. A metabolic kitchen in the Clinical Research and Trials Unit of Mayo Clinic's Center for Clinical and Translational Science conducts the protocols.

Fitness testing

Researchers evaluate study participants' cardiorespiratory fitness through graded exercise testing — for example, using a treadmill or cycle ergometer. We use indirect calorimetry to continuously measure:

• Oxygen consumption (VO₂).
• Carbon dioxide production (VCO₂).
• Ventilation.
• Respiratory exchange ratio.

This allows us to determine maximal oxygen uptake (VO₂ max) or peak oxygen uptake (VO₂ peak).

Glucose stable isotope tracers for measuring glucose disposal in the context of insulin sensitivity

We infuse labeled glucose — for example, [6,6-²H₂] glucose — to assess glucose kinetics, including endogenous glucose production and peripheral glucose uptake. This is usually combined with insulin clamp techniques to quantify insulin-stimulated glucose disposal.

Hot box arterialized blood sampling

In this technique, a study participant places a hand in a box heated to 131 degrees Fahrenheit (55 degrees Celsius) to increase blood flow. This allows venous blood to become "arterialized" and approximate arterial blood composition so we can measure gases, glucose and metabolites without direct arterial puncture.

ICG blood flow

We use indocyanine green (ICG), an intravenously administered dye, to measure regional blood flow — for example, in the legs — or splanchnic blood flow based on dye dilution and optical detection.

Insulin clamps for measurements of skeletal muscle and adipose insulin sensitivity

This is the gold standard hyperinsulinemic-euglycemic clamp technique, involving continuous insulin infusion with variable glucose infusion to maintain euglycemia (90 to 95 mg/dL). This approach enables quantification of whole-body skeletal muscle insulin sensitivity and adipose tissue insulin sensitivity when combined with fatty acid tracers.

Metabolic rate

We measure resting energy expenditure and substrate oxidation using indirect calorimetry based on oxygen consumption and carbon dioxide production. We also assess total energy expenditure and substrate oxidation during activity or experimental interventions.

Mixed meal tolerance testing

We give a fasting participant a standardized mixed nutrient meal containing carbohydrate, fat and protein — for example, Ensure Plus — at approximately 40% of resting metabolic rate. We then conduct serial blood sampling to measure glucose, insulin and C-peptide. We also perform other procedures or take other measurements, such as fat biopsies or blood flow measurements, to measure how the body processes the mixed nutrient meal. This technique is sometimes combined with hot box techniques to obtain arterialized blood samples.

Nasogastric tube placement

This technique involves insertion of a small, flexible tube through the nasal passage into the stomach or duodenum for controlled nutrient delivery. It enables precise timing and dosing of enteral interventions in metabolic experiments.

Oral glucose tolerance testing

We administer a standardized glucose solution — typically 75 grams — to a fasting individual and then conduct serial blood sampling to measure plasma glucose levels over two hours. This technique is sometimes combined with hot box techniques to obtain arterialized blood samples. This test evaluates how effectively the body processes glucose. Its primary purpose is to diagnose diabetes and prediabetes.

Radioactive isotope fatty acid tracers

We give study participants radiolabeled fatty acids — for example, ¹⁴C- or ³H-labeled fatty acids — in a mixed meal to quantify meal fat oxidation and storage. These tracers allow us to precisely quantify fatty acid oxidation, tissue-specific uptake and storage in conjunction with adipose tissue biopsy techniques.

Skeletal muscle biopsies

A percutaneous biopsy of thigh skeletal muscle — typically vastus lateralis — is performed under local anesthesia using a suction-modified Bergstrom needle technique. Samples can be used to evaluate muscle lipids and signaling pathways.

Stable isotope fatty acid tracers for measuring systemic lipid flux

We administer nonradioactive, isotopically labeled fatty acids — for example, ¹³C- or ²H-labeled fatty acids — to quantify whole-body lipid kinetics in vivo. These tracers enable measurements of fatty acid appearance and disappearance rates under fasting or experimental conditions. When combined with insulin clamps, the tracers can provide data for calculating insulin concentration that suppresses free fatty acid release by 50%. This calculation, known as IC₅₀, is an estimate of adipose tissue insulin sensitivity.

Strength testing (leg and hand)

We quantitatively assess muscular strength, such as handgrip strength, through standard dynamometry, and test leg extension using a Keiser leg extension machine.

Subcutaneous adipose tissue biopsy (abdomen and thigh)

We perform minimally invasive collection of subcutaneous adipose tissue from the abdominal and thigh regions using needle aspiration with a small liposuction cannula under sterile conditions and local anesthesia. This method yields intact adipose samples for downstream analyses including histology, gene and protein expression, lipid metabolism assays, and ex vivo functional studies.

¹³³Xenon washout for adipose tissue blood flow

A localized injection of radioactive ¹³³Xenon into adipose tissue is followed by measurement of its washout rate. The clearance kinetics provide a quantitative measurement of adipose tissue blood flow at rest or during metabolic interventions.