How GLP-1 medications work and why lifestyle matters –Part 1 – Nutrition and Physical Activity

June 30, 2026 - Behnaz Atree, MD

GLP-1 medications have recently been getting widespread public and clinical attention. This blog has been written to help you understand the science behind them, their history and why lifestyle is the foundation. It is not an endorsement of these medications for everyone, nor an encouragement to seek them out without medical supervision.

GLP-1 receptor agonists are FDA approved for adults with type 2 diabetes requiring blood sugar management, and for chronic weight management in adults with a BMI of 30 or higher -or a BMI of 27 or higher when associated with a weight-related health condition such as hypertension, dyslipidemia, cardiovascular disease, or obstructive sleep apnea. They should always be used under medical supervision.

GLP-1 stands for glucagon-like peptide-1 – it is a hormone your body makes naturally. It is produced by specialized L-cells lining your intestine and is released into the blood stream every time you eat. In response, the pancreas releases insulin, the stomach slows its emptying, and the brain begins registering feeling full. It is your gut’s way of signaling to the rest of the body that you have eaten and that the body now needs to respond.

The GLP-1 medications making headlines today – semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound) – are engineered analogs of this hormone. They bind to the same receptors as natural GLP-1 but are structurally modified to resist rapid breakdown. They last days to weeks rather than the 1-2 minutes that our own natural GLP-1 survives in circulation.

A DISCOVERY OVER 100 YEARS IN THE MAKING

The story begins in the early 1900s, when British physiologists William Bayliss and Ernest Starling made a landmark observation: the intestine secretes a chemical

messenger that travels through the blood to trigger the pancreas. They named it secretin. It was the first proof that the gut and pancreas communicate hormonally, and this is what gave birth to the field of endocrinology.

Decades later, in the 1920s, researchers noticed something puzzling: swallowing glucose produced a dramatically larger insulin response than infusing the same amount of glucose directly into the bloodstream. The gut, it seemed, was sending an additional insulin-amplifying signal beyond what blood sugar could explain. This phenomenon became known as the Incretin effect – and identifying its molecular source became one of the quests of 20^th century metabolic research.

By the 1980s, two gut hormones were identified as the primary drivers: GIP

(glucose-dependent insulinotropic polypeptide) and GLP-1. The therapeutic potential was obvious, but the main obstacle was that the enzyme DPP-4 destroyed GLP-1 within minutes of its entering the blood stream, resulting in it lasting only a couple of minutes in our circulation, negating its benefits.

The breakthrough came in the 1990s when endocrinologist Dr John Eg isolated a peptide from Gila monster venom – exendin-4 – that mimicked GLP-1’s actions, but was resistant to DPP-4. It became the structural basis for exenatide (Byetta), the first FDA-approved GLP-1 receptor agonist in 2005. What followed was a generation of increasingly refined molecules – longer acting, more potent, and applicable not just to diabetes but also to weight loss. In 2017, semaglutide (Ozempic) was approved, and from 2021 to 2023, semaglutide (Wegovy) and tirzepatide (Zepbound) were approved for obesity management. Tirzepatide (Mounjaro/Zepbound) deserves a special mention. It is a dual agonist – it activates both GLP-1 receptors and GIP-receptors.

This dual action appears to produce greater weight loss than GLP-1 alone.

MECHANISMS OF ACTION – What do these medications actually do in your body?

GLP-1 receptor agonists (class of drugs including semaglutide and tirzepatide) work through several pathways. Understanding these, helps explain their benefits as well as side effects.

SIGNALS THE BRAIN – They activate hypothalamic pathways (in the brain) that reduce appetite and food cravings, especially for high-fat, calorie dense foods.

SLOWS STOMACH EMPTYING – They delay gastric emptying, so food moves more slowly into the intestine which increases satiety after meals.

REGULATES INSULIN – They stimulate the release of insulin (in a glucose dependent manner – only when blood sugar is elevated – reducing hypoglycemia risk).

SUPPRESSES GLUCAGON – They lower glucagon (the hormone that raises blood sugar), which helps smoothen out blood glucose fluctuations after meals.

Why is nausea one of the most common side effects? The most common side effect –nausea, and occasionally vomiting – is a result of slowed gastric emptying. The stomach is fuller for longer than the body expects.

Why Lifestyle Still Forms the Foundation

GLP-1 agonists are tools for blood sugar control and weight loss, but they do not address the root causes of metabolic disease. They also come with some limitations, making lifestyle habits the foundation for weight management.

Clinical studies show that when GLP-1 medications are stopped, a large percentage of patients regain a significant portion of the lost weight. The medications suppress appetite while you take them, but they do not rewire the metabolic environment that contributed to weight gain in the first place.

Additionally, approximately 10-20% of people have a suboptimal response to these medications, as biology is not uniform and medications alone are usually not the full answer.

Below are the first 2 Lifestyle Medicine Pillars – Nutrition and Physical Activity –why they matter and how to optimize them when you are on a GLP-1 agonist or even for general weight loss.

Nutrition – Whole food, Protein Adequate Nutrition

GLP-1 medications reduce appetite, but they do not choose what goes on your plate. When calories drop significantly, what you eat becomes more important than ever.

Nutrition is the substrate your body uses to preserve muscle, regulate blood sugar, fuel the brain, and heal tissue.

When appetite is suppressed on GLP-1 medications, total caloric intake is significantly reduced. This is the mechanism behind weight loss, but it is important to keep in mind that fewer calories mean fewer opportunities to meet your macronutrient and

micronutrient needs. If those smaller meals are composed primarily of

ultra-processed foods, refined carbohydrates, or low protein snacks, the body pays a price, even if weight loss goals are being achieved.

Below are 4 nutritional priorities for patients on GLP-1 therapy:

#1 – Protein: Protect Your Muscles

Every significant caloric deficit whether it is from diet, medication or surgery causes some degree of loss of lean body mass alongside fat loss.  Decreased muscle and bone mass from GLP-1 induced weight loss can compromise mobility, balance and

functional independence. It can lower basal metabolic rate, making weight gain more likely. Also, patients who discontinue GLP-1 medications mostly regain fat rather than muscle which compounds the risk of sarcopenia (muscle loss). Protein intake can help counteract this as it helps your body build and repair muscles. The target for patients on GLP-1 therapy is 1.2 to 1.6 grams of protein per kilogram of body weight per day. This is substantially higher than typical recommendations.

HIGH QUALITY PROTEIN SOURCES TO PRIORITIZE:

• Fatty Fish (salmon, sardines, mackerel) Lean poultry (chicken, turkey)
• Legumes (lentils, chickpeas, edamame) Greek yogurt and cottage cheese
• Eggs and egg whites

#2 – Fiber: Supports the microbiome, Helps boost natural GLP-1, and Manages GI side effect (constipation)

GLP-1 medications slow gastric emptying and blunt glucose spikes after meals. Dietary fiber reinforces and extends these effects. The target is 25-35 grams of dietary fiber per day and to try to get a mix of soluble and insoluble fiber. Soluble fiber (found in oats, legumes, flaxseed) forms a viscous gel in the gut that slows glucose absorption and stabilizes blood sugar. Insoluble fiber from vegetables and whole grains adds bulk that supports satiety and prevents constipation.

Beyond helping with blood glucose regulation, fiber is the primary fuel for the gut microbiome – the trillions of bacteria that reside in the colon. A diverse, fiber-rich microbiome produces short-chain fatty acids such as butyrate, propionate, and acetate, which have direct anti-inflammatory effects, support the intestinal barrier, and actually stimulate natural GLP-1 secretion from L-cells in the gut. So, eating more fiber may boost the body’s own GLP-1 production (even if in a small amount), complementing the medication.

FIBER RICH FOODS TO BUILD THE MEAL AROUND

• Leafy greens and cruciferous vegetables Berries (blueberries, raspberries)
• Oats, barley and whole grains Lentils and beans
• Avocado
• Chia seeds and flaxseed

#3 – Be mindful of micronutrients

GLP-1 medications slow stomach emptying, which can affect the absorption of certain micronutrients like calcium, iron, vitamin B12 and vitamin D. Also eating less means every bite counts! Focus on foods rich in nutrients but lower in empty calories, such as lean poultry, legumes, Greek yogurt, nuts, seeds, vegetables, whole grains. Minimize ultra-processed foods which are calorie-dense and nutrient poor.

Make sure to include calcium-rich foods like leafy greens, dairy and vitamin D rich foods like fatty fish in your meals and snacks.

Pair vitamin D rich foods with healthy fats like avocado or olive oil for better absorption. Include iron rich foods like lentils, chickpeas and spinach in your meals and snacks.

For better absorption, pair iron-rich foods with vitamin C (like oranges, bell peppers) and avoid consuming them at the same time as calcium-rich foods, tea, or coffee.

#4 – Stay hydrated

GLP-1 medications can decrease thirst perception alongside appetite. This can create a dehydration risk especially when combined with nausea, vomiting, or diarrhea.

Aim for:

• At least 8 glasses (64 fl oz) of water daily
• Include water-rich foods (fruits, vegetables, soups) Monitor for signs of dehydration (dizziness)

Strategic Meal Patterns: How and when to Eat

The way food is consumed matters just as much as what is consumed.

• Small, frequent meals (every 3-4 hours rather than large meals).
• Eat slowly, and stop when full.
• Avoid nighttime eating.
• Avoid skipping meals even if appetite reduces. Not eating worsens nausea.

Physical Activity – Resistance Training helps preserve muscle mass

Every weight loss intervention – surgery, medication, diet – causes some muscle mass loss. Preserving muscle improves resting metabolism, functional strength, bone density, and insulin sensitivity. Resistance training is the primary defense.

Aim for at least 2-3 sessions per week targeting major muscle groups. Examples of resistance exercises include bicep curls, shoulder presses, banded rows, banded squats. Try to have at least 48 hours between sessions for muscle recovery. Start with 2-3 sets of 8-12 reps per exercise and increase gradually.

Before starting any new exercise routine, consult your healthcare provider. If you need help with proper form and technique, consult a certified trainer.

Other physical activity strategies:

Post-meal walk (30-45 minutes after eating, 15-30 minute brisk walk) can blunt glucose spikes and enhance GLP-1 signaling.

Sitting breaks throughout the day (2 min brisk walk every 20-30 minutes) can increase post-prandial (after meals) GLP-1.

GLP-1 medications are powerful tools for blood sugar management and weight loss that work by mimicking a naturally occurring hormone. They help regulate appetite, blood

sugar, improve satiety, and support weight loss. However, they work best when combined with healthy lifestyle habits.

We discussed how nutrition and physical activity help preserve muscle mass and support metabolism. In our next blog we will discuss why Sleep, Stress Management, Connectedness and Avoidance of Risky Substances matter when on GLP-1 medications, how to manage side effects and some overall practical lifestyle strategies when on GLP-1 medications.

Current FDA-approved indications for GLP-1 medications in weight management include adults with BMI>or equal to 30, or a BMI >or equal to 27 with at least one weight-related comorbidity (type 2 diabetes, hypertension, dyslipidemia, obstructive sleep apnea, or cardiovascular disease). For type 2 diabetes management, the threshold is set by glycemic criteria.

These medications are not appropriate for individuals with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2 (MEN2). They should be used with caution in pregnancy.

A thorough evaluation with a physician who understands your full medical history, labs and goals is essential before starting and while you are on these medications.

Sources:
The evolution of endocrinology. Clinical Endocrinology. 2005. Wilson JD.

British Journal of Clinical Pharmacology. 2026. Kamath S, Chan NSL, Joyce P

Behnaz Atree, MD

Dr. Behnaz Atree has been a practicing Primary Care physician in Raleigh, NC, for over 20 years. Dr. Atree has become certified in Lifestyle Medicine in 2022 as well as Health and Wellness Coaching in 2023. She is excited to integrate her experience in Internal Medicine with her training in Lifestyle Medicine and Health Coaching to provide evidence-based, therapeutic lifestyle interventions through Carolina Lifestyle Medicine.

Click here to read more about Dr Behnaz Atree, MD