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How Do GLP-1s Work for Weight Loss? A Doctor and Dietitian Explain
Webinar Summary
GLP-1 medications are a class of injectable drugs that mimic hormones your body naturally produces to regulate appetite, blood sugar, and digestion. They work primarily by slowing how fast food moves through your stomach, signaling your brain to eat less, and helping your pancreas manage blood sugar more effectively.
Clinical research shows that semaglutide produces an average of 17.4% total body weight loss, while tirzepatide — a newer dual-action option — averages around 22.5%. These results typically develop over one to two years, with the most significant losses occurring in months three through six.
Side effects are real but manageable for most people. Nausea affects roughly half of patients, usually in the first few weeks, and tends to improve on its own. More serious risks — including pancreatitis — are rare but worth discussing with your provider before starting.
These medications work best as a tool, not a permanent replacement for lifestyle change. They’ve been in active research and clinical use since the early 1990s, with over 30 years of safety data.
Meet the Experts
Dr. William YiBoard-certified general surgeon specializing in general and bariatric surgery, practicing in Northeastern Pennsylvania. Dr. Yi has extensive clinical experience prescribing and managing GLP-1 medications alongside bariatric surgical care, and regularly counsels patients on candidacy, safety, and long-term weight management.
Kristen Kirkpatrick, MS, RDRegistered dietitian with over 20 years of clinical experience working primarily in weight management, fatty liver disease, and nutritional psychology. Kristen works with patients across life stages — with a significant focus on perimenopausal and postmenopausal women — helping them build sustainable dietary habits alongside GLP-1 therapy.
Watch the Full Webinar
Dr. Yi and Kristen Kirkpatrick covered the most common questions patients bring to their first appointment. If you prefer to read, everything below is pulled directly from this conversation.
GLP-1 stands for glucagon-like peptide-1. Specifically, these are hormones your body already produces — released by your intestines and pancreas in response to eating. The medications used for weight loss are either direct versions of this hormone or modified forms designed to last longer in your system.
Here’s what they actually do inside your body, according to Dr. Yi:
Slow down digestion — food moves through your stomach more slowly, so you feel full longer
Signal your brain to eat less — they act on appetite centers to reduce the drive to eat
Regulate blood sugar — they prompt the pancreas to release insulin and reduce glucose production in the liver
Dr. Yi uses a simple analogy: calories are like coal, your eating habits are the train delivering it, and your exercise is the factory burning it. In other words, GLP-1 medications slow the train — they make you eat less. They don’t directly burn fat. Instead, they reduce how many calories come in, which is what creates the deficit that drives weight loss.
Additionally, these medications have been in clinical research since the early 1990s, originally developed to treat type 2 diabetes. The weight loss benefits were discovered when diabetic patients started losing significant amounts of weight as a side effect. As a result, there are now over 30 years of safety data behind these drugs.
How Much Weight Can You Realistically Lose?
Research shows meaningful results — but these are clinical averages, not guarantees. Results depend on your starting weight, whether you’re making dietary and lifestyle changes, and how long you stay on the medication.
f you’re in perimenopause or postmenopause and feel like weight loss has become impossible no matter what you do — you’re not imagining it, and you’re not doing anything wrong.
When estrogen drops during menopause, belly fat tends to increase and your body becomes significantly more resistant to losing it through diet and exercise alone. Kristen Kirkpatrick, who works primarily with this population, estimates that roughly 99% of her female GLP-1 patients are peri or postmenopausal. In fact, it’s one of the most common and clinically appropriate use cases for this medication.
Why Menopause Makes Weight Loss Harder
Estrogen decline shifts fat storage to the abdomen. This isn’t a willpower problem. It’s a hormonal one.
Additionally, insulin sensitivity decreases. Blood sugar regulation becomes harder, increasing risk for prediabetes and type 2 diabetes — exactly what GLP-1s are designed to address.
Cardiovascular risk goes up after menopause. As a result, women see increased risk for heart disease. GLP-1 medications have documented cardiovascular benefits that are especially relevant here.
As Kristen put it during the webinar: “GLP-1s work with your hormones, not against them.” For women whose bodies have shifted metabolically, that’s a meaningful distinction.
Furthermore, there’s also early data suggesting GLP-1 medications may reduce risk of dementia and Alzheimer’s — a concern that often motivates her patients who have seen a parent go through cognitive decline.
“I would say of all the patients I have on these drugs, 99% of them are women who are perimenopausal or menopausal. It is very likely once we get into menopause that because of the reduction of estrogen, we increase belly fat. It becomes so much harder to lose weight.”
— Kristen Kirkpatrick, MS, RD
GLP-1 Side Effects: What to Expect and What to Do
Most of the side effects are a direct result of how the medication works — not signs something has gone wrong, according to Dr. Yi.
Side Effect
How Common
Why It Happens
Nausea
~44–50% of patients
Food moves more slowly through the stomach; usually resolves by week 5
Diarrhea
Common, especially early
Digestive timing is disrupted; can alternate with constipation
Constipation
Common
Gut motility slows down
Heartburn
~10% of patients
Slower stomach emptying; worsens existing reflux
Rare but Notable Risks
Gallstones: Slightly elevated at 1.6% vs. 0.7% in the general population — but this appears to be a consequence of rapid weight loss itself, not the medication directly.
Pancreatitis: About 1% of users vs. 0.05% in the general population. Not something to dismiss — worth an explicit conversation with your provider before starting.
Ready to find out if GLP-1 therapy is right for you?
Schedule a consultation with our team to review your health history and goals with a provider who specializes in weight management.
Nutrition on GLP-1s: Why What You Eat Really Matters
Since you’re eating less, every bite has to count more. Kristen Kirkpatrick put it plainly: if you think you can just eat less of whatever you already eat and come out ahead, you’re likely to lose muscle, feel terrible, and miss the whole opportunity the medication gives you.
In other words, stop focusing on the number on the scale. Focus on body composition — how much fat vs. muscle you’re carrying. A lower number that includes significant muscle loss isn’t a win.
Prioritize Protein at Every Meal
Muscle loss is a real risk on GLP-1s, especially with rapid weight loss. For this reason. protein at every meal is your main defense.
Eggs, cottage cheese, Greek yogurt
Lean meats, fish, poultry • Beans and lentils (protein and fiber in one)
Tempeh — fermented, so it also works as a probiotic
Grains with protein: farro, quinoa (for example, cook farro and lentils together and store for the week as a bowl base)
Exact targets vary by weight, activity, and kidney function. As a general guideline, aim for 0.8 to 1.1 grams of protein per kilogram of body weight, adjusted by your provider.
Fiber and Complex Carbs
With digestion already slowing, constipation is a common issue. However, fiber helps significantly. Focus on:
Whole fruits with the skin on (that’s where the fiber is)
Starchy vegetables, legumes, nuts and seeds
Complex carbohydrates over refined ones
Healthy Fats
Extra virgin olive oil
Fatty fish (salmon, sardines)
Walnuts — the only nut with significant omega-3s
Nut butters without added sugar
Hydration
When your appetite is suppressed, it’s easy to forget to drink too. Aim for light yellow urine as a simple hydration check. Additionally, hydrating foods — spinach, fruits, cottage cheese, milk — count toward your daily fluid intake.
Supplements to Discuss With Your Provider
Omega-3 fatty acids (most people fall short of recommended intake)
Vitamin D (widely underdosed in the general population)
B12, especially if eating less animal protein
A general multivitamin
Probiotic or prebiotic to support gut health
Supplemental fiber if constipation becomes a persistent issue
Are You a Good Candidate? What Dr. Yi Looks For
A prescription requires a clinical evaluation — but here’s what Dr. Yi considers when a patient comes in asking about GLP-1 therapy.
You May Be a Good Candidate If…
You’ve made multiple genuine attempts to lose weight through diet and exercise and haven’t been able to sustain results
You have insulin resistance or prediabetes
You’re experiencing menopause-related abdominal weight gain that isn’t responding to lifestyle changes
Your weight is creating other health risks — joint pain, cardiovascular risk, elevated blood sugar — that make it harder to exercise or stick to a diet in the first place
You’re dealing with alcohol intake you’d like to reduce (some patients notice decreased desire to drink)
You are genuinely willing to make dietary and lifestyle changes alongside the medication — not instead of them
GLP-1 Medications Are Not Appropriate If…
You have a personal or family history of medullary thyroid cancer or MEN syndrome (multiple endocrine neoplasia) — the medications may increase thyroid cancer risk, based on animal studies
You have active or severe kidney disease
You have a significant history of disordered eating — appetite suppression can exacerbate these patterns in ways that are harmful
You’re looking for a shortcut and have no intention of changing how you eat or move — the medication won’t create lasting results without those changes
You are pregnant or trying to become pregnant
The World Health Organization recently updated its guidelines to include GLP-1 medications as a legitimate option for obesity treatment — a significant shift from its previous lifestyle-only stance. But as both Dr. Yi and Kristen emphasized: these aren’t right for everyone, and a thorough provider evaluation is the necessary first step.
Common Concerns — Answered Honestly
Will I gain all the weight back when I stop?
The honest answer from Dr. Yi: it depends entirely on what you did while you were on the medication.
If you were on the medication for one to two years and made no dietary or lifestyle changes, stopping is likely to result in weight regain. As a result, your body will return to where it was.
On the other hand, if you built genuine habits — better eating, regular movement, a sustainable calorie balance — many patients maintain their weight loss after stopping, and some continue losing. The medication is the spark plug. Ultimately, the lifestyle change is the engine.
Is this just a shortcut?
No. Kristen pushed back on this framing directly during the webinar.
“We have to stop stigmatizing the fact that people may take these drugs because they’re trying to lose weight.”
— Kristen Kirkpatrick, MS, RD
For someone who has been fighting weight gain through hormonal shifts, metabolic challenges, or years of diet culture, a medication that quiets the constant mental noise around food isn’t a shortcut. It’s a tool. In fact, the World Health Organization now agrees — and updated its guidelines accordingly.
What will the first few weeks actually feel like?
Probably rough. Dr. Yi was upfront about this: many patients describe the first four to six weeks as miserable. Irritability, fatigue, and slow initial weight loss are all common — and all explainable.
Here’s what’s happening: when you’re in a caloric deficit, your body reads it as a threat and releases more cortisol. It’s literally fighting what you’re trying to do. That’s why early mood changes and low energy are so common — your body is under real stress.
The good news: for most people, this does improve after that initial window. Mood stabilizes, energy returns, and the benefits start to feel real. Getting through the first four to six weeks is the hardest part.
A Real Patient’s Experience
Dr. Yi invited a friend — Aaron — to share his experience live on the webinar. Specifically, Aaron started GLP-1 therapy with OrderlyMeds about six months before the recording, partly after watching his wife see real results.
Lost roughly 25 pounds over six months
The first week was tough — he dealt with both constipation and diarrhea
After that, things leveled out quickly
Noticed more fatigue on days when he wasn’t getting enough protein
Started running and was training for a marathon at the time of the webinar (Dr. Yi noted Aaron’s previous “exercise” had been walking 18 holes of golf)
Overall, he reported significantly improved mood, more energy with his kids, and better resilience through the winter months
“Losing the weight, not getting winded going up steps, being able to play with my three little kids and have lots of energy — I just feel a lot better.”
— Aaron, customer
Want to have this conversation with a provider who specializes in GLP-1 therapy?
Our team includes a board-certified bariatric surgeon and registered dietitian who can assess whether this is the right fit for your health history and goals.
GLP-1 medications work by slowing down how fast food moves through your digestive system, signaling your brain to reduce appetite, and helping regulate blood sugar. You eat less because you feel full longer and the mental drive to eat decreases. They don’t directly burn fat — they reduce caloric intake, which creates the deficit that produces weight loss.
How much weight can I expect to lose on a GLP-1?
Clinical research shows an average of around 17.4% total body weight loss with semaglutide and approximately 22.5% with tirzepatide. These are averages — individual results vary based on starting weight, dietary changes, activity level, and how long you stay on the medication. Most significant weight loss happens between months three and six.
What are the most common GLP-1 side effects?
Nausea is the most common, affecting about 44–50% of patients — usually in the first few weeks and often resolving by week five. Diarrhea and constipation are also common and can alternate. Heartburn affects about 10% of users. These side effects are mostly a direct result of how the medication slows digestion. Eating smaller, more frequent meals can help manage nausea.
Are GLP-1 medications safe?
GLP-1 medications have been in clinical research since the early 1990s — originally to treat type 2 diabetes — and have over 30 years of safety data. The overall safety profile is considered strong for most patients. The main risks worth discussing with your provider are pancreatitis (about 1% of users) and thyroid concerns for those with a personal or family history of medullary thyroid cancer or MEN syndrome.
Will I gain the weight back when I stop taking GLP-1 medications?
It depends on what you do while you’re on the medication. If you use the time on GLP-1 therapy to build sustainable dietary and exercise habits, many patients maintain their weight loss after stopping. If no lifestyle changes are made, weight regain is likely. The medications are a tool to enable change — not a permanent substitute for it.
Are GLP-1s a good option for menopause-related weight gain?
Yes — this is one of the most common and clinically appropriate use cases. When estrogen drops during menopause, belly fat increases and weight becomes significantly harder to lose through diet and exercise alone. GLP-1 medications work with the hormonal environment rather than against it, and also address the increased cardiovascular and metabolic risks that come with menopause. Roughly 99% of one expert dietitian’s female GLP-1 patients are peri or postmenopausal.
How do I know if I’m a good candidate for GLP-1 therapy?
Good candidates typically have a history of struggling to lose weight through lifestyle changes alone, are dealing with insulin resistance or metabolic issues, or are experiencing health risks tied to their weight. People with a history of medullary thyroid cancer, MEN syndrome, active kidney disease, or significant disordered eating are generally not appropriate candidates. A provider evaluation is the necessary first step.
What should I eat while taking GLP-1 medications?
Since you’ll be eating less overall, every bite needs more nutritional value. Focus on lean protein at every meal to protect muscle mass, fiber-rich foods to prevent constipation, and healthy fats like olive oil and fatty fish. Common supplements to discuss with your provider include omega-3 fatty acids, vitamin D, B12, and a probiotic. Working with a registered dietitian while on GLP-1 therapy is strongly recommended.
How long do I have to take GLP-1 medications?
There’s no single answer. Some patients take them for one to two years and transition off after establishing lifestyle changes. Others may need a longer course. The goal is to use the medication as a starting point — to lose weight, build habits, and eventually maintain without it. Cost is also a practical factor: these medications are expensive long-term, which is another reason not to rely on them indefinitely.
What is the difference between semaglutide and tirzepatide?
Both are weekly injectable GLP-1 medications used for weight management. Semaglutide activates GLP-1 receptors; tirzepatide activates both GLP-1 and GIP (a second gut hormone), making it a dual-action option. Clinical research shows tirzepatide produces slightly higher average weight loss — around 22.5% vs. 17.4% for semaglutide. The right choice depends on your health profile and provider’s recommendation.
Medical Disclaimer: This article is for informational purposes only and does not constitute medical advice. The content is based on a recorded webinar with a board-certified bariatric surgeon and registered dietitian. GLP-1 medications require a prescription and a clinical evaluation. Always consult a qualified healthcare provider before starting or stopping any medication.
