What Thinsulin Gets Right, and What It Can't Prove

Article 1 of 5 in Thinsulin, revisited. Evidence reviewed through September 7, 2026. Written for adults in a United States clinical setting.

A medicine helps your mood, but you feel hungry sooner after meals. Your clothes fit differently. Advice to try harder leaves you feeling blamed. That situation is common enough in psychiatric care that it is worth asking a bigger question: what would weight care look like if it took your whole life into account?

The Thinsulin Program: The Breakthrough Solution to Help You Lose Weight and Stay Thin tries to answer that question. Published in 2016, it pairs food rules with tools for changing eating habits. 1 This series explains what the book asks of readers and checks its claims against evidence available through September 7, 2026.

The useful starting point is that weight care should address more than a menu. The harder question is whether the book’s insulin theory and exact schedule have been shown to work as claimed. Those are two separate questions. A helpful routine does not prove every explanation offered for it.

Key takeaways

• The book’s strongest contribution is treating weight as a whole-life problem, not a menu problem. That part matches current care.
• Its core idea is that low insulin drives fat loss, and that raising insulin later resets the body. No controlled trial found in this review supports that.
• The results the book reports come from a clinic poster, not an independently verified trial. Key details are missing.
• Insulin is one part of a system. A normal insulin rise after eating is not evidence of harm.
• Some people need a clinician’s plan before any restrictive phase. That includes anyone on diabetes medicine or lithium, and anyone with kidney disease, a pregnancy, breastfeeding, or a history of an eating disorder.

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Start with the person, then discuss the plan

Your body size cannot tell someone how you eat, how much you move, or what kind of person you are. A number on a scale cannot show your full health either. Weight care may involve symptoms, blood pressure, blood sugar, sleep, strength, comfort, and the demands of daily life. Your goals belong in that discussion. 2

Current U.S. guidance treats obesity as a long-term condition with several causes. Genes, body systems, medicines, other health problems, and daily surroundings can all matter. The American Diabetes Association’s 2026 obesity standards ask for a full check-up of every adult diagnosed with overweight or obesity. That check-up covers medical, behavioral, and social factors. It also rates how advanced the condition is. What it finds shapes the plan and the follow-up. 2

There is also a different route to consider early. If eating brings marked fear, repeated loss of control, purging, or exercise meant to undo food, ask for an eating-disorder assessment. These illnesses occur at many body sizes. A stricter weight-loss plan may be the wrong next step. A past eating disorder also deserves a private conversation before any new restriction. 3

Who wrote the book, and what does the name mean?

The book has three authors: Charles Nguyen, MD, Tu Nguyen, MD, and Mary Ann Marshall. The publisher describes Charles Nguyen’s psychiatric background and Tu Nguyen’s internal-medicine training and weight-management practice. Marshall is a writer and editor. 1

The name joins three ideas: thinking, being thin, and insulin. The authors ask readers to think about how food affects insulin instead of counting calories. They then connect those choices to goal setting, meal planning, and changing unhelpful thoughts. That is their framework. It is not a complete account of how bodies regulate weight. 1

Their psychiatric angle matters. A plan can look simple on paper and become very hard during depression, long shifts, poor sleep, or a change in appetite. Still, other evidence-based weight programs also include behavior and mental health. This book did not invent those parts of care. 4

The two phases in plain language

The Active Phase is the book’s loss-focused stage. Its usual calendar runs about four months. It asks for three main meals and two snacks a day. It removes grains and sweets, limits which fruits and nuts are allowed, and builds main meals around selected proteins and vegetables. The book describes this as lowering insulin to promote fat loss. 1

The Passive Phase shifts the goal toward keeping weight steady. Across about three months, the authors gradually add back portions of foods excluded earlier. They call these “enjoyment foods.” The book also encourages activity and continued work on habits. It claims that raising insulin during this stage prepares the body for another loss phase. This review did not locate evidence establishing that reset mechanism or its timing. 1

Maintenance is a worthwhile subject in its own right. Learning how to keep eating, moving, resting, and getting support through a busy month has real value. But a calendar cannot tell every body when weight loss must stop, and these phases are not required stages of medical care.

What seems useful, and what needs checking

Reducing the number of daily decisions can make a plan easier to use. Having food ready can reduce long gaps caused by work or caregiving. Those are practical reasons a routine may help. They do not require a claim that a carrot blocks fat loss.

The distinction matters when a rule creates trouble. If a plan leaves you hungry, short of money, afraid of food, or unable to eat with other people, that is information for your care team. It is not proof that you lack commitment. A useful plan has to meet your nutrition needs and stay workable. 5

What do the program’s results actually show?

The book reports a clinic poster presented at a 2013 obesity conference. It describes average weight loss of 10.8%, or about 23 pounds, over an average of 86 days. Those are results reported by the book. They are not independently verified trial findings, and the original poster was not retrieved for this review. 1

That leaves major questions unanswered. How many people entered, and whose results were counted? Who stopped attending? What medicines were used, and was there a comparison group? The book’s separate statement that its clinics had treated more than 13,000 people is a historical claim about the practice. It is not the poster’s sample size. 1

Those missing details change what a reader can conclude. If results include only the people who stayed, the average may look very different from results for everyone who started. Without a comparison group, no one can separate the program from support, medicine, time, or other life changes. Without clear reporting of harms, no one can assume none occurred.

The book also describes a small 2015 series of patients who cycled through the phases. It does not fix these gaps or prove the reset theory. 1 Photos and personal stories can show what one person experienced. They cannot tell you your odds of benefit. Searches for this review did not locate a controlled trial of the exact program. That means the evidence was not found, not that no such study could ever exist.

Insulin matters, but it is not the whole explanation

Insulin is an essential hormone. It helps control blood glucose and affects how the body stores and uses fuel. Lowering insulin can change which fuel the body burns at a given moment. That does not mean lower insulin guarantees lasting loss of body fat, regardless of how much energy a person takes in and uses. 6, 7, 8

A large trial called DIETFITS compared a healthy low-fat approach with a healthy low-carbohydrate approach for a year in 609 adults without diabetes. The low-fat group lost 5.3 kilograms on average. The low-carbohydrate group lost 6.0 kilograms. The gap between them was not statistically significant. A measure of insulin release taken at the start did not identify which diet would work better for whom. The trial did not test this book’s program, and it does not mean every diet fits every person equally well. 9

You do not have to count calories to recognize that energy balance matters. A plan can change fullness, food choices, and intake without a tracking app. Article 2 explains this distinction and examines the book’s food categories.

Where psychiatric care can help

Some psychiatric medicines can affect appetite, weight, or blood sugar and fats. The effects differ across medicines and across people. Mood symptoms, sleep changes, and recovery itself can also change eating. A timeline can help a prescriber ask better questions, but timing alone does not prove what caused a change. 10

Bring a list of prescriptions, over-the-counter products, and supplements. Note roughly when appetite, sleep, energy, or weight changed. You do not need to weigh yourself to make that list. Also note other events, such as a new shift, an injury, caregiving, or losing access to regular meals.

A medicine review should weigh mental stability and metabolic health together. It may lead to monitoring, nutrition support, an added treatment, or a carefully chosen medicine change. It should not begin with stopping a helpful psychiatric medicine on your own. A 2025 guideline supports metformin to help prevent weight gain in selected people starting antipsychotic treatment. The certainty of that evidence is low, and this use is off-label in the United States, so it requires a prescriber’s judgment. 10, 11

Psychiatric care can also treat depression, anxiety, or an eating disorder that is making daily life harder. Therapy may help with thoughts, stress, and routines. It does not erase a medicine’s biological effects or guarantee a change in weight.

Current care has more than one valid route

Nutrition care, behavior support, prescription treatment when indicated, and metabolic or bariatric surgery can all be legitimate options. They may be used together. There is no need to complete this program before discussing other care. Surgical decisions require a personal assessment and long-term follow-up, and this book is not a required diet after surgery. 12, 13

The book’s 2016 medicine appendix should be read as history. For example, lorcaserin was sold as Belviq. In February 2020, the FDA requested its withdrawal after a safety trial showed a cancer signal. A medicine listed in an older book may no longer be an option at all. 14

If you use insulin or a medicine that can cause low blood sugar, a major change in food intake needs a monitoring and medicine plan. SGLT2 inhibitors such as dapagliflozin carry a ketoacidosis risk that rises with reduced food intake, a ketogenic diet, dehydration, or illness. Lithium safety can shift with changes in salt and fluid. Kidney disease, pregnancy, breastfeeding, frailty, and prior bariatric surgery also change nutrition needs. Discuss all of this before trying a restrictive phase. 15, 16, 5

What to do this week

Use W01, Goals and Care-Team Conversation, to name one thing you want to feel easier. It might be less afternoon fatigue, steadier meals at work, or less worry about food. Add the medicines and health issues you want reviewed, and bring it to your next visit.

If the timing of a change is unclear, try W02, Medication, Appetite, Sleep, and Weight Timeline. A few broad events are enough, and existing weight information is optional. Then ask, “What else could explain this, and what should we check first?” If writing it down makes you distressed, bring a spoken summary instead.

Frequently asked questions

Is Thinsulin the same as keto? Not exactly. Its usual plan restricts grains and sweets but includes fruit, vegetables, and some dairy and legumes. It does not set one carbohydrate target for everyone. Whether someone enters ketosis depends on what they actually eat. Do not assume a label tells you a diet’s medical risks. 1

Is insulin the whole explanation for weight change? No. It is one part of a system that also involves appetite, energy needs, other hormones, medicines, and daily conditions. A normal insulin rise after food is not proof of harm. 8

Can I try it while taking psychiatric medication? Discuss it with your prescriber first. Review appetite changes, nutrition needs, monitoring, and any medicine that becomes less safe with restriction or dehydration. Keep taking prescribed medicine as directed unless your clinician changes the plan.

Who needs a clinician’s plan first? Anyone considering substantial restriction should discuss whether it fits. That is especially important with diabetes medicines, lithium, kidney disease, prior bariatric surgery, pregnancy, breastfeeding, frailty, or eating concerns. This restrictive adult program is not a plan for children or teens.

Must I buy the book to use the worksheets? No. The worksheets are original educational aids. They help you prepare questions and plan support. They are not validated tests, and they do not require you to follow the book.

Related reading on NP FADY

• Article 2: Red Light, Green Light: Thinsulin’s Food Rules
• Article 5: Cravings, CBT, and the Thought That Ruins a Day
• Companion worksheets: W01 and W02 for this article (PDF, four pages), or the full Small steps for food, health, and care workbook (PDF, 21 pages)

About the book

The Thinsulin Program: The Breakthrough Solution to Help You Lose Weight and Stay Thin contains the authors’ complete 2016 program. This series adds an evidence review through September 7, 2026. The book is available from Amazon. NP FADY earns nothing from that link, and buying the book is not required for care or for these worksheets.

References

1. Nguyen C, Nguyen T, Marshall MA. The Thinsulin Program: The Breakthrough Solution to Help You Lose Weight and Stay Thin. Da Capo Press; 2016. ISBN 978-0-7382-1873-1. Program description, author background, and the clinic results reported by the authors.

2. American Diabetes Association Professional Practice Committee for Obesity. Screening, Diagnosis, Evaluation, and Staging of Obesity in Adults: Standards of Care in Overweight and Obesity-2026. BMJ Open Diabetes Research & Care. 2026;13(Suppl 1):e006247. doi:10.1136/bmjdrc-2026-006247

3. American Psychiatric Association. Practice Guideline for the Treatment of Patients With Eating Disorders, 4th edition. American Psychiatric Association Publishing; 2023. Guideline summary: American Journal of Psychiatry. 2023;180(2):167–171.

4. US Preventive Services Task Force. Behavioral Weight Loss Interventions to Prevent Obesity-Related Morbidity and Mortality in Adults: US Preventive Services Task Force Recommendation Statement. JAMA. 2018;320(11):1163–1171.

5. National Institute for Health and Care Excellence. Overweight and obesity management. NG246. Published January 14, 2025; last updated 2026. United Kingdom.

6. Mann E, Sunni M, Bellin MD. Secretion of Insulin in Response to Diet and Hormones. Pancreapedia. Version 2.0, December 23, 2020. doi:10.3998/panc.2020.16

7. Hall KD, Farooqi IS, Friedman JM, et al. The energy balance model of obesity: beyond calories in, calories out. American Journal of Clinical Nutrition. 2022;115(5):1243–1254. doi:10.1093/ajcn/nqac031

8. Hall KD, Guo J, Courville AB, et al. Effect of a plant-based, low-fat diet versus an animal-based, ketogenic diet on ad libitum energy intake. Nature Medicine. 2021;27(2):344–353. doi:10.1038/s41591-020-01209-1

9. Gardner CD, Trepanowski JF, Del Gobbo LC, et al. Effect of Low-Fat vs Low-Carbohydrate Diet on 12-Month Weight Loss in Overweight Adults and the Association With Genotype Pattern or Insulin Secretion: The DIETFITS Randomized Clinical Trial. JAMA. 2018;319(7):667–679. doi:10.1001/jama.2018.0245

10. American Diabetes Association, American Psychiatric Association, American Association of Clinical Endocrinologists, North American Association for the Study of Obesity. Consensus development conference on antipsychotic drugs and obesity and diabetes. Diabetes Care. 2004;27(2):596–601.

11. Carolan A, Hynes-Ryan C, Agarwal SM, et al. Metformin for the Prevention of Antipsychotic-Induced Weight Gain: Guideline Development and Consensus Validation. Schizophrenia Bulletin. 2025;51(5):1193–1205. doi:10.1093/schbul/sbae205

12. American Diabetes Association Professional Practice Committee. 8. Obesity and Weight Management for the Prevention and Treatment of Diabetes: Standards of Care in Diabetes-2026. Diabetes Care. 2026;49(Suppl 1):S166–S182.

13. Eisenberg D, Shikora SA, Aarts E, et al. 2022 American Society for Metabolic and Bariatric Surgery and International Federation for the Surgery of Obesity and Metabolic Disorders: Indications for Metabolic and Bariatric Surgery. Surgery for Obesity and Related Diseases. 2022;18(12):1345–1356.

14. US Food and Drug Administration. FDA requests the withdrawal of the weight-loss drug Belviq, Belviq XR (lorcaserin) from the market. February 13, 2020.

15. FARXIGA (dapagliflozin) tablets, for oral use. Prescribing information. AstraZeneca Pharmaceuticals LP; revised June 2026. Section 5.1, Diabetic Ketoacidosis; Section 5.2, Volume Depletion.

16. LITHOBID (lithium carbonate) extended-release tablets. Prescribing information. ANI Pharmaceuticals, Inc. DailyMed record last published August 24, 2026.

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This article is for education and does not replace care from your own clinician. Do not change prescribed medicine or begin a restrictive eating plan without discussing your needs with your care team. Evidence checked through September 7, 2026.

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