(208) 385-7711

Dr. Mark Holthouse, MD, IFMCP
Chief Medical Officer

Meet The FMI Team

At FMI, we’re committed to pioneering the field of functional and integrative medicine. Our focus is on delivering top-quality care to our patients, emphasizing prevention of chronic diseases and getting to the root causes of health issues. We take a team-based and patient-focused approach, where our expert providers work diligently to uncover the underlying reasons behind symptoms. Our unwavering dedication to excellence and patient satisfaction has established us as leaders in the field, setting the benchmark for outstanding healthcare.
Adult Functional Providers
Michael Sermon, PA-C
Medical Director
Adult Functional Provider
Meridian Wellness Center
Amy Ray, FNP, IFMCP
Adult Functional Provider
Boise Clinic
Elizabeth Hingley, NP-C, IFMCP, CDCES
Adult Functional Provider
Boise Clinic
Gavin Guard, PA-C, CISSN
Adult Functional Provider
Virtual
Janessa Tenney, PA-C, IFMCP
Adult Functional Provider
Meridian Clinic
Karen Callagy, PA-C, IFMCP
Adult Functional Practitioner
Boise Clinic
Julie Franden, DNP, NP-C
Adult Functional Provider
Meridian Clinic
Adult Primary Care Providers
Christa Inzer Castillo MSPAS, PA-C, MPH
Adult Primary Care Provider
Meridian Clinic
Kaitlin Cooley, FNP-C
Adult Primary Care Provider
Meridian Clinic
Sheridan Jones, DNP, FNP-C
Adult Primary Care Provider
Meridian Clinic
Women's Health Functional Providers
Jessica Bennett, CNM, APRN
Women's Health Functional Provider
Meridian Clinic
Kristin Gomes, APRN-CNM
Women’s Health Functional Provider
Meridian Clinic
Tamra Geryk, FNP-C, IFMCP
Women’s Health Functional Provider
Boise Clinic
Pediatric Providers
Dr. Mario Brus, MD
Functional Pediatrician
Meridian Clinic
Aaron Dykstra, DNP, FNP-C
Pediatric Functional Provider
Meridian Clinic
Olivia Mangeac, PA
Pediatric Functional Provider
Meridian Clinic
Nadia Kravchuk, DNP, FNP-C
Pediatric Functional Provider
Meridian Clinic

Mark Holthouse, MD, ABoIM, IFMCP

Dr. Mark Holthouse MD is the Chief Medical Officer for Functional Medicine Of Idaho and FMI Center For Optimal Health. Dr. Holthouse is only seeing patients through FMI Center For Optimal Health. To inquire about being seen by Dr. Holthouse, follow this link to the New Client Inquiry form, here.

Areas of Expertise:

• Expertise in both Men’s & Women’s Hormone Management and Bioidentical Hormone Replacement Therapy: pellets etc.

 • Expertise in thyroid and adrenal gland imbalances

• Expertise in reversing pre-diabetes, diabetic medicine, metabolic syndrome

• Optimizing body composition: lean muscle and belly fat removal / Intermittent Fasting

 • Expert in managing cholesterol, cardiac, and blood pressure from a holistic perspective

 • Expertise in anti-aging and cellular senescence management

 • Expertise in environmental medicine: heavy metals, mold diseases, mast cell activation syndromes

 • Expertise in holistic approaches to autoimmune and gut health

 • General Functional Medicine

Michael Sermon, PA-C

Michael Sermon is the Medical Director of Functional Medicine of Idaho since 2023. He earned his Bachelor’s Degree in Human Movement Science at Utah State University. He then continued his education at Saint Francis University earning his Master of Physician Assistant Science. While working in family practice, urgent care, and emergency medicine in the rural areas of Texas and Oregon, Michael discovered that lifestyle modification and root-cause medicine is the key to disease prevention and healing.

After experiencing the effectiveness of root-cause medicine in his own life, and the lives of his patients and family, it became clear to Michael that the functional medicine model is key to lifelong health. He believes that patients should be highly involved with their own health care decisions, with guidance and expertise from the FMI team. Michael integrates traditional primary care with functional medicine in order to achieve preventative and restorative care for patients. He is currently working on functional medicine certification.

Michael enjoys hiking, biking, ice hockey, and many other sports. He spends his free time with his wife and children, enjoying the small things life has to offer.

Areas of Expertise:

  • Foundational Functional Lifestyle approach to primary care
  • Cardiometabolic Health
  • Men’s Hormones
  • Autoimmune conditions

Amy Ray, FNP, IFMCP

Amy Ray is board certified by the American Nurse Credentialing Center as a Family Nurse Practitioner. Amy has over 20 years of healthcare experience and is passionate about seeking out the root causes of chronic “dis-ease” and empowering her patients to reach and maintain a state of optimal wellness. She has her undergrad in Nutrition Science from UC Davis and her Master’s degree in Nursing from MGH Institute of Health Professions in Boston, MA.

She first started looking in to functional medicine after many years of being disillusioned with allopathic medicine when her chronically ill patients rarely ever felt better with conventional treatment. She became fully committed to functional medicine after her father was diagnosed with stage 3 chronic kidney disease and was told he would be “monitored and then treated when it got worse- and it would get worse.” Luckily, he was not satisfied with that answer and came to her for help and guidance using her new found functional approach. He is at is healthiest now, and she has never looked back. 

Amy has extensive experience in metabolic syndrome, insulin resistance, hormone imbalance, gut health, headaches, and autoimmune issues.  She truly believes that food is medicine and that lifestyle changes are foundational for reversing chronic “dis-ease.”  She believes our bodies are incredibly smart and protective and seeks to partner with her patients to find ways for their unique bodies to find the wellness and balance they once knew. She is an IFM Board Certified Functional Medicine Provider.

Outside of the office, Amy enjoys fitness, volunteering, gardening, traveling and all things outdoors. She and her husband moved to the area in hopes of enjoying all the wonderful outdoor opportunities Idaho has to offer.

Specialties include:

  • Gut
  • Hormones
  • Autoimmune
  • Headaches

 

Elizabeth Hingley, NP-C, IFMCP, CDCES

Elizabeth Hingley is an accomplished Family Nurse Practitioner, who earned her MSN degree from Georgetown University in Washington, DC in 2013. Her passion for patient care and dedication to her profession led her to pursue additional certifications. In 2022, she received her IFMCP through IFM.org, and she has been a Certified Diabetes and Education Specialist since 2011. Elizabeth has gained valuable experience in urgent care and endocrine management, specializing in diabetes, thyroid, testosterone, and weight management. She noticed that even with traditional medicine, some patients still experienced persistent symptoms, which led her to explore alternative therapies and focus on lifestyle management to address the underlying causes. Elizabeth is committed to patient education and empowering them to take ownership of their health, working with them as partners on their health journey. In addition to her passion for health and wellness, Elizabeth enjoys traveling with her loved ones, trail running, hiking, and exploring the great outdoors.

Areas of Expertise:
Diabetes
Thyroid
Weight Concerns

Gavin Guard, PA-C, MPAS, CISSN, Pn1

Gavin Guard believes that the average doctor visit is not giving patients the time and support they deserve. Gavin graduated summa cum laude from Whitman College with a bachelor’s in biochemistry before completing graduate medical school training at the University of Colorado. His main clinical focuses include gastrointestinal disorders, thyroid and hormone health, as well as metabolic disease like diabetes, high cholesterol, and heart disease. Aside from patient care, Gavin is also publishing medical literature in the functional medicine field. He wakes up every morning to help patients find lasting solutions to their health so that they can experience hope and feel restored. When not in the clinic or reading papers, you can find him spending time with his wife and two young girls or pumping iron in the weight room.

Areas of Expertise:

  • Digestive concerns (IBS, SIBO, IBD, reflux, bloating, diarrhea, constipation, abdominal pain)
  • Complications of poor GI health (fatigue, brain fog, hormone imbalance, autoimmunity)
  • Longevity and preventive health (metabolic health, heart health, hormone replacement, weight loss, exercise prescription, fasting, advanced diet protocols)

Janessa Tenney, PA-C, IFMCP

Janessa Tenney is a board certified Physician Assistant who offers in-person and telemedicine primary and functional care for adults at the Functional Medicine of Idaho Meridian Wellness Center.

Early in her career as a Physician Assistant, Janessa was introduced to functional medicine while working at a private practice in Monterey, California, where she witnessed first-hand how patient outcomes could be drastically improved if the patient was properly educated about their lifestyle and nutrition choices. She began studying functional medicine and started to implement its principles into her conventional medical practice. Janessa joined the Functional Medicine of Idaho team in 2021, and now combines her love for patient education with her passion for functional medicine in order to change patients’ lives every day. 

Janessa earned her Bachelor of Science in Public Health from Brigham Young University – Idaho, and her Master of Medical Sciences in Physician Assistant Studies from Salus University. She is currently working towards her certification with The Institute for Functional Medicine. 

Outside of the clinic, Janessa enjoys hiking, paddle boarding, kayaking, spending time with her friends and family, watching movies, and trying new food.

Karen Callagy, PA-C, IFMCP

Karen Callagy received her Bachelor’s degree in Kinesiology from Pennsylvania State University in 1997. After working in Physical Therapy, as a PTA for several years, she went on to obtain her M.S. in Physician Assistant Studies at Arizona School of Health Sciences in 2005. She began her PA career in Family Medicine, eventually transitioning to Urgent care, as well as a brief stint in Oncology.

In all these settings, she began to realize that prescribing medications was not enough to make patients better and in many cases only perpetuated the problem. In her personal life, she was dealing with family members with autoimmune diseases that conventional medicine could not help, because diet was never addressed. After discovering the Institute of Functional Medicine in 2014, there was no turning back. Not only has she helped her own family but innumerable patients with the help of IFM. She continues to work towards her IFM certification, specializing in thyroid and gut health.

Karen firmly believes in “mind, body and spirit” and that each of these aspects must in balance for her patients to achieve their maximum health potential. She immensely enjoys going on the journey to wellness with her patients and believes it “takes a village” to accomplish this, ie. Nutrition staff, life coaching, and in some cases counseling.

In her personal life, she enjoys outdoor activities with her husband and 3 children, on the mountain where they reside, with their bunnies and Bernese Mountain Dog.

Areas of Expertise:

  • Thyroid
  • Gut Health

Julie Franden, DNP, NP-C

Julie is a board certified Family Nurse Practitioner with over 12 years of experience, providing acute and primary care for patients of all ages.

Julie was born and raised in Boise. She completed her bachelors of nursing at Boise State University. In pursuit of higher education Julie completed her masters and doctorate at George Washington University. Her doctorate is in palliative care, focusing on providing a well rounded approach to patient care. Her goal is to provide the highest quality of life for all her patients, to work in a collaborative relationship and support individual goals.

She is continuing her education through The Institute For Functional Medicine with the goal of obtaining her Functional Medicine Provider certification.

In her free time, Julie spends time with her family including her husband Joe and their two sons. They enjoy camping, hiking, and skiing.

Christa Inzer Castillo MSPAS, PA-C, MPH

Christa Inzer Castillo is a board certified Physician Assistant, with 14 years of experience in  family practice, who offers primary and acute care for adults and children. She loves the opportunity to get to know entire families and develop relationships with her  patients. While trained in western medicine she has long infused a whole person and natural  approaches to achieve best patient outcomes.  

Personal experience, specifically a mother who has responded poorly to the traditional western  medical approach, but used whole body approaches to find answers inspired Christa to begin  the process of understanding root cause medicine. The desire to help answer “why” is this  going on in the body and “how” to help the body heal has become a passion. The process of  teasing out each person’s unique puzzle is fascinating and rewarding, especially when you start  to see health restored.  

Christa grew up in the Treasure Valley, graduated from Meridian High School, earned her  Bachelor of Science in Biology from the College of Idaho. In 2008 she earned her Master of  Science in Physician Assistant Studies and Masters of Public Health from Touro University in  Vallejo, California.  

Outside of the clinic, Christa enjoys spending time with her husband and 3 children. You can  find them outside working on numerous projects with chickens, goats, rabbits, dogs, cats, and  gardening, or hiking and exploring the great state of Idaho. She also loves to serve in her  church and squeeze in a swim.

Kaitlin Cooley, FNP-C

Kaitlin Cooley is a board certified Family Nurse Practitioner who offers primary and acute care for adults and children. She has experience working with all ages of patients from neonatal to geriatric care. 

As a Boise native, Kaitlin enjoyed a collegiate softball career in front of her friends and family at The College of Idaho. Kaitlin graduated from the college with a bachelors degree in Health Sciences. She later attended Idaho State University and obtained her nursing degree. After working as a registered nurse in the hospital, Kaitlin discovered she wanted to help patients optimize their health in the primary care setting by building foundational wellness. As a result, Kaitlin applied to Northwest Nazarene University and later graduated with honors with her Family Nurse Practitioner degree.

Kaitlin is passionate about providing quality care and helping patients feel their best. She practices an individualized, patient-centered, and science-based approach when meeting with patients and believes the best outcomes are met when patient and provider work in collaboration. She is continuing her education through The Institute For Functional Medicine with the goal of obtaining her Functional Medicine Provider certification.

Kaitlin is married to her husband, Matt, and has two sons. They enjoy spending time outside golfing, hiking, and running around with the kids.

Sheridan Jones, DNP, FNP-C

Sheridan Jones has her Doctorate in Nursing Practice and is a board-certified Family Nurse Practitioner. With over 12 years of experience in healthcare she offers primary and acute care for adults and children. Sheridan has always lived an active lifestyle with a passion for health, wellness, and fitness. She was a Division I college athlete, playing soccer while studying nursing. While she was a student athlete she earned her Bachelor’s of Science in Nursing at Gonzaga University in 2011. 
After several years as a bedside nurse, she felt the calling to advance her career. With a desire to focus on preventative medicine, and improvement of patient outcomes through education and empowerment, she went on and graduated with her Doctorate and Family Nurse Practitioner degree in 2021 from Gonzaga University. With several years working in various Emergency, Hospital, and Acute Care settings she learned early on that this approach of band-aid medicine did not align with her own life, values, and practice. She discovered the healing powers of lifestyle modifications and root cause medicine.
During her time as a student at Gonzaga and a nurse practitioner in the field she learned the meaning of ‘magis’. This concept means “to strive beyond the status quo”. She joined the team at Functional Medicine of Idaho to do just that. To dive deeper into disease prevention, optimizing wellness, and healing through dietary and lifestyle modifications. As a lifelong learner, she continues her education through the Institute for Functional Medicine with the goal of obtaining her Functional Medicine Certification. 
Sheridan is married to her husband, Dan. They have a bird dog, Nix. Together they love cooking, time in the mountains, and exploring the outdoors: hunting, camping, trail running, rafting, skiing, spending time with family and friends.

Jessica Bennett, Certified Nurse Midwife/APRN

Jessica Bennett graduated with a Bachelors of Science in Nursing from the University of Vermont in 2003. After practicing as a nurse for ten years, she felt an unwavering desire to continue her education and pursue an advanced practice degree as a Certified Nurse Midwife. Graduating with honors from Frontier Nursing University in 2014, Jessica set out as a Certified Nurse Midwife and has never looked back.

Over the past seven years, Jessica has provided women’s health primary care, with a particular emphasis on hormone imbalance, including thyroid conditions, PCOS, infertility, sexual pain, and hormone replacement therapy for pre-menopausal and post-menopausal women. She is also experienced in full-scope well woman/primary care, including natural childbirth, birth control consultations, family planning, IUD and Nexplanon insertions and removals, GYN annual exams, problem visits, medication management, thyroid issues, hormone balancing, gut health, natural approach to managing mood disorders, and diet and exercise management for weight loss.

Her approach to women’s healthcare is focused on prevention, total body wellness, and patient education. With a true passion for health, wellness, and empowering women, she is immensely grateful to have the opportunity to pursue her passions every day.

Kristin Gomes, APRN-CNM

Kristin is a Certified Nurse Midwife.  She received a bachelor’s of science in nursing from California State University San Bernardino.  After working as a registered nurse in transplant, oncology, and palliative care Kristin switched her focus to gynecology, labor, and birth.  Recognizing the need to emphasize health, wellness, and prevention in our culture, she saw an opportunity to impact the health of women and their families through education focused, more personalized, family centered care. Thus, Kristin pursued a graduate degree in nurse midwifery at New York University and graduated with honors in 2014.  She has practiced as a nurse midwife in the Treasure Valley since 2015.

Throughout her years of practice Kristin has always strived to provide an inclusive and holistic approach to healthcare. She aspires to meet each woman where they are and collaborate with them on their health journey.  She has seen the profound difference in treating a symptom vs treating the cause while supporting the body.  The desire to support the innate healing and protective qualities of the body through evidenced based care led to her discovery of functional medicine.  In late 2020 she began her training through the Institute for Functional Medicine which she completed in the winter of 2022.  At Functional Medicine of Idaho alongside the community of practitioners, nutritionists, nurses, and health coaches Kristin has the opportunity to provide a personalized and integrative women’s health experience focused on individualized wellness. 

Kristin feels deeply connected to nature.  When she’s not in the mountains camping, hiking, kayaking, or fishing you can find her tending her garden beds or on her yoga mat.  Her favorite season is winter, preferably one with lots of snow, and her happy place is on her skis with her husband and daughter.

Tamra Geryk, FNP-C, IFMCP

Tamra Geryk is a board-certified Family Nurse Practitioner specializing in Women’s Health. 

Tamra has over a decade of experience in Integrative and Functional Medicine. An educator at heart, Tamra is passionate about creating change in how health care is provided and perceived. Her work with patients is based on health promotion, disease prevention and education rooted in dietary and lifestyle modifications to address core clinical imbalances. As a practitioner, Tamra works collaboratively with her patients and team to promote optimal health by focusing on the fundamental factors that influence every patient’s experience of health and disease. Tamra’s journey into functional medicine began while seeking root cause medicine to address her own digestive and energy imbalances over 15 years ago. 

Tamra earned her Bachelor of Science from the University of Massachusetts Amherst and completed a Master in Science specializing in health promotion, disease prevention, and behavior modification. During her graduate studies, she completed her fieldwork at Canyon Ranch in Lenox, MA, and her health coaching certification through the Institute for Integrative Nutrition. Tamra completed her Functional Medicine training through the Institute for Functional Medicine in 2019 and went on to pursue her passion for health and healing by earning her Master’s degree in Nursing from Frontier Nursing University in 2021. Tamra is currently pursuing further Women’s Functional & Integrative studies through Aviva Romm’s Practitioner Training Program.

In her spare time, Tamra enjoys spending outdoors with her family and her dogs, meditating, cooking, and gardening.

Mario Brus, MD

Dr. Mario Brus obtained his medical and pediatric specialty training at Loma Linda University in Southern California. He is a board-certified pediatrician and maintains his Fellow of the American Academy of Pediatrics (FAAP) designation with his ongoing commitment to lifelong learning and advocacy for children.

His current emphasis is pediatric functional medicine, which aims to find underlying causation for pediatric chronic conditions. He addresses the root cause of these conditions with appropriate laboratory testing, genetic testing, and by emphasizing lifestyle and nutrition changes, as well as appropriate nutritional supplementation. This functional approach to pediatrics allows Dr. Brus to partner in the care of your child by listening to your concerns and making your child’s health his primary focus.

He believes in a conservative use of drugs and an aggressive encouragement of lifestyle and dietary changes that strongly impact body and brain function. Overall, his goal is to fix health issues at their source.

Aaron Dykstra, DNP, FNP-C

Aaron Dykstra is a board certified Family Nurse Practitioner with a Doctor of Nursing Practice degree. He offers pediatric primary care, including well-child checks and acute visits, in the Pediatric Department of the Functional Medicine of Idaho Meridian Wellness Center.

Functional and alternative therapies were a part of Aaron’s life from a young age, and he has implemented these principles into his conventional medicine practice throughout his career. Aaron has more than 8 years of experience in a variety of medical disciplines, including pediatrics, obstetrics, mental health, and nutrition. He has practiced in rural health clinics in California and Oregon. For the last 5 years, Aaron has had a passion for working with children and implementing positive change through the family unit. Aaron joined the Functional Medicine of Idaho Pediatric Team in 2021. His enthusiasm for educating children and parents about living a healthy lifestyle allows him to provide preventative and acute care for infants, children, and adolescents. 

Aaron obtained his Bachelor of Science in Nursing at Brigham Young University. He earned both his Master’s of Science in Nursing and Doctor of Nursing Practice through the University of Arizona. He has obtained a Family Herbalist and Family Nutritionist certifications through The School of Natural Healing by Dr. Christopher. He is currently working towards his certification with The Institute for Functional Medicine.

Outside of work, you will find Aaron spending time with his wife and 5 kids, mountain biking, running, or camping in the backyard. Aaron is a big fan of Master Chef and enjoys cooking.

Olivia Mangeac, PA-C

Olivia Mangeac is a certified Physician Assistant who offers pediatric primary care, including well child checks and acute visits, in the Functional Medicine of Idaho Pediatric Department. 

Olivia began her career working in Urgent Care at St. Alphonsus, where she practiced as a Physician Assistant for 5 years. Throughout her time in Urgent Care, she became interested in root cause medicine and chronic illness prevention. Wanting to provide a wider scope of care for her patients by diving deeper and addressing more than surface-level symptoms, Olivia began studying functional medicine. She joined the Functional Medicine of Idaho Pediatric Team in 2021. Her passion for taking a proactive approach to healthcare allows her to provide preventative and acute care for infants, children, and adolescents. 

Olivia earned her Bachelor of Science in Biology from Northwest Nazarene University, and her Master of Medical Science from Arcadia University.

In her spare time, Olivia enjoys snowboarding, hiking, backpacking, and spending time with her husband and daughter. 

Nadia Kravchuk, DNP, FNP-C

Nadia Kravchuk is a board certified Family Nurse Practitioner with a Doctor of Nursing Practice degree. She offers functional pediatric primary care, including well-child checks and acute visits, in the Pediatric Department of the Functional Medicine of Idaho Meridian Wellness Center.

Nadia and her family immigrated to the United States in 1989 where they first settled in Oregon and then moved to Idaho in 2001. Complementary medicine practices were embedded into her lifestyle at a young age, and she has implemented these principles into her conventional medicine practice throughout her career. She has more than 15 years experience in a variety of medical environments, including emergency room, intensive care unit, pediatrics, obstetrics and gynecology, family practice, and aesthetics.

Nadia joined Functional Medicine of Idaho so that she can combine functional principles with the foundations of conventional medicine to address the underlying causes of disease and promote optimal wellness. As an avid gardener, beekeeper, and sustainable living enthusiast, she understands the importance and role of optimizing nutrition, sleep, physical, spiritual, and emotional well-being. She has a passion for pediatric functional medicine and understands that early recognition and interventions can correct imbalances, prevent chronic illness, and improve overall outcomes for children.

Nadia obtained her Bachelor of Science in Nursing at Northwest Nazarene University. She earned both her Master’s of Science in Nursing and Doctor of Nursing Practice through Frontier Nursing University. In 2017, she was the recipient of the HCA Excellence in Nursing Award. She is currently working towards her certification with The Institute for Functional Medicine.

Outside of work, you will find Nadia working on her urban homestead, hiking, foraging, camping, snowboarding, and spending time with her husband and her dog, Wolfy. She is also fluent in both English and Russian.