The purpose of this research study is to understand how breath is related to nutritional status. The procedures involved in this study include blood and breath sampling, questionnaires about health history, medications, nutritional status and diet, and a physical examination. Breath markers will be compared between individuals with and without malnutrition and be compared to indicators of malnutrition. Some individuals will undergo an interventional study involving 2 days of consuming study beverages and fasting along with providing additional breath samples to see if the breath changes in response to short-term changes in nutritional status.

Research Summary: This research involves a cross-sectional study investigating whether breath molecules (in particular ammonia and nitric oxide) are related to the presence and magnitude of malnutrition as measured by the gold-standard nutrition focused physical examination (NFPE). It also involves an interventional study in a subset of cross-sectional participants looking at whether acute changes in nutritional status through anabolic feeding protocols or fasting protocols is related to short term changes in breath molecules.

Purpose of the Research: The purpose is to identify early evidence of breath biomarkers of malnutrition. It uses a combination of breath analysis and current malnutrition screening tools (questionnaires).

Inclusion Criteria:

1. Age: 18-95 years
2. Malnutrition group (Cross-sectional study only); not involved in intervention: Diagnosed with malnutrition (verified in medical history)

Exclusion Criteria:

1. Chronic kidney, liver or pulmonary disease
2. Anabolic steroid use other than testosterone (e.g., oxandrolone)
3. Patients judged unsuitable for enrollment by the study medical investigator
4. Pregnant women or women who are nursing
5. Unable or unwilling to consume study beverages or fast for 24 hours each arm

External investigators may request additional data access, which will be shared according to institutional policy with appropriate data sharing agreements.

Upon reasonable request.

According to institutional policy.

The randomization scheme will be blinded to the PI and biostatistician. Due to the intervention (feeding vs fasting), the participant and other study staff cannot be blinded.