GLP-1 Diet — 4 traits of those who use it well

What is GLP-1 — a 35-year revolution that started with lizard venom

GLP-1 (glucagon-like peptide 1) is a hormone our body secretes from the small intestine when we eat. In the 1980s, Jean-Pierre Raufman at the US NIH discovered that the venom of the Gila monster (a venomous lizard of the US Southwest) increased cAMP in pancreatic cells 50–60 fold. In 1992, John Eng at the Bronx VA Hospital isolated Exendin-4 — 53% identical to human GLP-1 — from that venom. Human GLP-1 has a half-life of just 1–2 minutes, too short, but Exendin-4 is not degraded by the DPP-4 enzyme and lasts for several hours. This discovery led to the 2005 FDA approval of the first GLP-1 drug, exenatide (Byetta), and 35 years later it has become the powerful obesity medications we know as Wegovy and Mounjaro. In 2012, the US Congress awarded this research the Golden Goose Award — "a case where seemingly odd research brought major benefits to society."

Reference · Eng J et al. 1992 J Biol Chem 267(11):7402 / Drucker 2025 Nat Rev Drug Discov (IF 122.7)

Shared mechanism — how every GLP-1 drug works

Wegovy, Mounjaro, Saxenda, and orforglipron all work on the same basic principle. ① They stimulate the appetite center in the hypothalamus (especially the GLP-1R neurons of the DMH) to suppress appetite — and according to research by Professor Hyung Jin Choi's team at Seoul National University (Kim 2024 Science), they even activate the "preingestive satiation" circuit, where you feel full just by seeing food. ② They slow gastric emptying so fullness lasts longer, and ③ they promote glucose-dependent insulin secretion from the pancreas while suppressing glucagon. As a result, total calorie intake falls by 16–39% and weight naturally drops. You can only use these drugs well once you understand precisely that they are not "fat-burning drugs" but "drugs that keep you from eating."

Reference · Holst JJ. 2007 Physiol Rev (IF 37.6) / Kim KS et al. 2024 Science 385:438 (서울대 최형진)

Why visceral fat drops first — the most positive effect

The most striking effect of GLP-1 drugs is that they reduce visceral fat more than total fat. In the STEP 1 DXA substudy (140 people), Wegovy users' total fat fell -19.3% while visceral fat fell -27.4%. A meta-analysis of 30 RCTs (Liao 2023) also confirmed that GLP-1RAs significantly reduce visceral fat (SMD -0.59) and liver fat (WMD -3.09%). Because visceral fat is a key driver of hepatic insulin resistance, cardiovascular disease, and fatty liver (NAFLD), this result is very positive for health. The mechanisms are ① hypothalamus → sympathetic nerves → stimulation of visceral fat β-receptors, ② breaking the visceral-liver vicious cycle through improved insulin sensitivity, and ③ activating brown fat (BAT) plus promoting browning of white fat. This is the biggest difference from a simple weight-loss drug.

Reference · STEP 1 DXA / Liao J et al. 2023 PLOS ONE (메타분석 30 RCTs, n=1,736)

Muscle is lost too — that's why protein matters

The natural side effect of losing weight is common to all diets. When calories run short, the body breaks down not just fat but also muscle, bone density, and water for energy. In a meta-analysis of 22 RCTs (2024), 25–40% of the weight lost with GLP-1RAs was lean mass. What's interesting is that an animal comparison study by Jeromson 2025 (J Physiology) found that, at the same calorie deficit, the muscle-loss pattern of semaglutide and of simple calorie restriction was nearly identical — meaning GLP-1 is not a "muscle-burning drug" but rather this is "the effect of the calorie deficit itself." The solution is simple: ① enough protein at 1.5–2 g per kg of body weight, ② prioritize leucine-rich protein (whey, eggs, chicken breast), and ③ resistance training 2–3 times a week. These three cut the rate of muscle loss to less than half.

Reference · 22 RCT 메타분석 2024 / Jeromson 2025 J Physiology / Shah 2025 J Physiol Commentary

After discontinuation — the real diet begins after you stop the drug

The biggest challenge of GLP-1 dieting is the year after stopping. In the S-LiTE follow-up study (Jensen 2024), the drug-only group regained an average of 6.3 kg (70%+ of the weight lost) within a year, while the group that exercised regained the least, and the exercise-plus-drug group regained about 2.5 kg less than the drug-only group. An even more striking finding came from Holt 2025 (Obesity) — only the group that exercised for a year increased late-postprandial endogenous GLP-1 secretion by +37%. The drug supplies GLP-1 from outside; exercise restarts our body's own "GLP-1 factory." That is why discontinuation prep should begin not in the final month, but while the weight loss is still going well.

Reference · Jensen et al. 2024 eClinicalMedicine / Holt et al. 2025 Obesity (S-LiTE)

Why it matters more for Korean women — skinny fat and SMAS

Korean women carry two extra risks in GLP-1 dieting. First, their skinny-fat rate is the highest in East Asia (about 24.5%) — they look thin yet have a body-fat percentage over 30% or insufficient muscle mass. Use GLP-1 in this state and almost all of what you lose can be muscle. Second, their dermis is thicker than Westerners' and their SMAS (the superficial musculoaponeurotic system beneath the skin) is heavier (Daneshgaran 2024), so facial sagging can be more pronounced. That is why Korean women should ① check muscle mass with a body-composition test (such as InBody) before starting, ② set their protein target high, at 1.8 g/kg or more, ③ take collagen peptides daily, and ④ deliberately lose weight slowly. This is the pattern confirmed in the Rich Slim data.

Reference · InBody 2024 Annual Report (17개국 1억+ 측정) / Daneshgaran 2024

Rich Slim insight — which GLP-1 suits whom

GLP-1 drugs are a powerful tool, but they don't offer the same value to everyone. ① If you have medical obesity at BMI 30 or above, or BMI 27 or above with diabetes, hypertension, or dyslipidemia, Mounjaro (the strongest effect) offers the most value. ② If your BMI is 27–30 or your goal is 5–10% loss, Wegovy (with longer-accumulated data and well-known side effects) is the safe choice. ③ If diabetes management is the priority, Ozempic (low-dose semaglutide). ④ If injections are difficult and a smaller effect is enough, the soon-to-launch oral orforglipron. Whichever drug you use, the core is the same — protein + resistance training + discontinuation prep. Consult a clinician and decide only after reviewing your BMI, comorbidities, current medications, and pregnancy plans. The Rich Slim book and tools will be by your side, free, at every stage.

Reference · 오랜 시간 현장 데이터 + 의료진 협업

Manage rebound and risk from the early stage of weight loss

While on GLP-1, fullness intensifies and your meal portions may naturally shrink. The problem is when protein, fiber, and water shrink along with them. Only by setting meal standards from the early stage of weight loss does a structure remain that your body can hold up under after you stop the drug.

Losing weight well and managing health well are different things

If you judge success by the result of weight loss alone, a sunken face, muscle loss, fatigue, constipation, and exercise avoidance can surface later. Rich Slim looks at the density and resilience after weight loss as its standard, rather than the number.

What you can do next, right now, on Rich Slim

Check your current risk level with the self-test, set your daily protein and water standards with the 3.3.3 calculator, and then continue reading the muscle-loss and discontinuation chapters of the book. The service is currently free, and you can use the book, calculator, and community right away.