Red Light, Green Light: Thinsulin's Food Rules

Article 2 of 5 in Thinsulin, revisited. Evidence reviewed through September 7, 2026. Written for adults in a United States clinical setting.

Picture a salad with lettuce, chickpeas, chicken, tomatoes, bread pieces, and dressing. Is that one kind of food or several?

That question sits at the center of The Thinsulin Program. The authors ask readers to sort a mixed dish into groups before choosing what to eat. 1

Sorting ingredients is a useful skill. The next step needs more care. A simple food system cannot tell the whole story of nutrition, hunger, or weight. This article explains the book’s traffic-light rules and shows where current evidence calls for a wider view.

Key takeaways

• Sorting a mixed meal into its parts is a genuinely useful habit. Grading those parts as forbidden or allowed is a different move, and a weaker one.
• Protein raises insulin too. The book’s claim that protein foods do not is too simple.
• Where a plant stores its fuel (root, leaf, or kernel) does not predict its health value.
• Large trials find no reliable weight advantage for cutting carbohydrate compared with a balanced approach over one to two years.
• The warning that artificial sweeteners inevitably drive cravings and weight gain goes past what research shows.

Zoom

A few words that make the science easier

Carbohydrate is a broad food component. It includes sugars, starches, and fiber. Sugars are small units. Starch is made of linked sugar units that digestion can break apart. Fiber includes carbohydrates that human digestive enzymes do not fully break down, and some fiber is used by gut microbes instead. These forms do not all act the same way in the body. 2

Glucose is a sugar carried in your blood and used for energy. Your body can also make glucose, so food is not its only source, and not everything you eat becomes glucose. Insulin is a hormone made in the pancreas. It helps control blood glucose and affects how the body stores and uses fuel. Insulin resistance means certain tissues respond less well to insulin, so the body may need to make more of it to do the same work. 3, 4

An insulin rise after a meal is often normal. The goal is not to push insulin as low as possible. People who need prescribed insulin must never reduce or skip it to try to lose fat.

Protein can also prompt insulin release. That is one reason the book’s claim that protein foods do not raise insulin is too simple. A hormone response is not a moral rating of a meal. 5

Energy balance does not require calorie counting

Over time, changes in stored body energy depend on energy entering and leaving the body. That fact does not mean eating and weight sit under simple conscious control. Appetite, medicine, sleep, food access, and the body’s changing needs all affect both sides of that equation. 6

It also does not mean you must log every bite. Some people make useful changes through regular meals, different food choices, or practical support. Others find a form of tracking helpful. The method should fit the person.

Burning fat for fuel is also different from losing stored body fat. If a diet contains more fat, more of the fat being burned may simply come from that day’s food. A short-term change in which fuel you burn cannot by itself tell us whether body fat will fall over months. 7

The book’s five groups

The book sorts food into five teaching groups: sweets, fruits, grains, vegetables, and proteins. These are the authors’ categories, not standard food groups and not a validated score of overall diet quality. Nuts and dairy sit inside the protein discussion but carry their own timing and portion rules. 1

The traffic-light idea works like this. Sweets, grains, and a handful of vegetables sit in the red group, excluded during the loss-focused Active Phase, whole grains included. Selected fruits and nuts sit in the yellow group, allowed in limited portions at assigned times. Selected proteins and vegetables sit in the green group, where the book permits more.

Two details are worth pausing on. The excluded vegetables include potatoes, corn, carrots, and beets. Avocado is excluded from the simple fruit list even though the book acknowledges its different nutrient profile. That gap is a clue. Some rules are chosen because they are easy to remember, not because every excluded food acts the same way in the body. 1

“Green” should also never mean ignore your needs. Protein choices vary widely in fat, sodium, and other nutrients. Kidney disease can change how much protein suits you. A dietitian can check whether a restricted plan supplies enough food, fiber, and nutrients for your body. 8

Why the plant shortcut has limits

The book uses where a plant stores its fuel as a memory aid. It favors leaves and flowering parts and discourages several roots, tubers, and kernels. The rule is memorable, but botanical location is not a reliable measure of health value. 1

Carrots and beets do not become unhealthy because they grow below ground. A potato, a serving of fries, and a bowl of lentils differ in structure, preparation, and what they provide. A broad plant rule misses all of that.

Current World Health Organization guidance favors carbohydrate sources such as whole grains, vegetables, fruit, and pulses, which include beans and lentils. It does not require every person to eat every food. Allergies, kidney disease, gut conditions, and personal needs still matter. The key point is that one program’s exclusion list is not evidence that a food prevents fat loss. 2

The same applies to a fresh-produce-only rule. Suitable frozen and canned produce can support a healthy eating pattern while lowering cost and waste. Check the label for added sugar or excess sodium when it matters. You do not need a fresh-produce budget to deserve nutrition care. 9

Glycemic index answers a narrow question

The glycemic index, or GI, compares blood-glucose responses to test portions of carbohydrate foods. Glycemic load adds in how much available carbohydrate a usual serving contains. These tools help with some food comparisons. They are not direct measurements of insulin, of body-fat change, or of a food’s full health value. 10

A food’s measured response can shift with portion, variety, ripeness, and cooking. A mixed meal adds more. Fat, protein, fiber, and the structure of the food all change how fast you digest it. Your own glucose response can differ from someone else’s for the same food.

That is why a “high-GI fruit” list should not harden into a fixed scientific category. Nor should one glucose reading decide that a food caused weight gain. Glucose monitoring has real medical uses, especially in diabetes, but a single curve does not measure long-term change in body fat.

What human diet trials can tell us

DIETFITS followed 609 adults without diabetes for a year. Participants received either a healthy low-fat or a healthy low-carbohydrate program, both with behavior support. The low-fat group lost 5.3 kilograms on average. The low-carbohydrate group lost 6.0 kilograms. That gap was not statistically significant. The insulin-release measure the researchers studied did not identify which approach would work better for whom. 11

People varied widely within each group. The trial did not hold adherence equal, did not test this book’s program, and cannot tell any individual which pattern to choose. What it does show is that “lower carbohydrate always works better” is too strong a claim.

A Cochrane review pooled 61 trials and nearly 7,000 people. Through one to two years, it found probably little or no average difference in weight loss between lower-carbohydrate and balanced-carbohydrate plans. That does not make food quality or individual fit irrelevant. It means a large lasting advantage from carbohydrate restriction alone was not established. 12

A different study kept 20 adults in a research unit. Each person tried two diets for two weeks each: a plant-based low-fat diet, and an animal-based ketogenic diet. People ate less energy on the low-fat diet despite its higher carbohydrate content. That challenges the simple prediction that more carbohydrate must drive more eating. The study was short and changed several things at once, so it cannot settle every version of the insulin theory. 13

Sweeteners need a more careful answer

The book warns that artificial sweeteners lead to cravings and more eating. Research does not support that as an inevitable result. Studies differ in which compound they use, what it replaces, and whether they measure a few hours of hunger or months of weight change. 1, 14

WHO’s 2023 advice against relying on non-sugar sweeteners for long-term weight control is a conditional recommendation based on low-certainty evidence. It does not apply to people who already have diabetes, and it is separate from chemical safety limits. It also does not advise replacing a diet drink with a sugary one. 14

In the SWEET trial, people swapped sugary products for ones made with sweeteners inside a supported eating plan. At one year, they had kept off about 1.6 more kilograms. That is a modest benefit for holding weight down. That is not the same as saying adding sweeteners to any diet causes weight loss. 15

An acute study of sucralose found more reported hunger compared with sugar, but no difference compared with water. It measured short-term responses, not future weight gain. A brain scan does not establish that your preferred drink is causing your cravings. Water and unsweetened drinks are useful options, and a substitution decision should fit your needs. 16

Read a mixed meal without grading it

Take the salad from the opening. Chicken and chickpeas provide protein, and chickpeas also provide carbohydrate and fiber. Lettuce and tomatoes add produce. Dressing may add fat and flavor. Bread pieces add grain. Instead of naming one ingredient as the reason a diet failed, ask whether the meal is enough, satisfying, affordable, and suited to your health needs.

At a restaurant, a fish taco may contain fish, a tortilla, cabbage, salsa, and sauce. The book’s Active Phase would remove the tortilla. A broader nutrition plan may keep it and review the whole meal instead. Either description should be honest about which framework it is using.

At home, lentil soup with carrots and bread offers several useful foods. The book would exclude some of those ingredients during its Active Phase. That does not make a family meal a problem to solve. A dietitian may help adjust amounts, ingredients, or timing while preserving what the meal means to your household and what it costs.

What to do this week

Choose one ordinary meal and use W03, Understand a Mixed Meal. Name its ingredients, what makes it satisfying, and what helps it fit your day. You may choose one addition or adjustment, or simply write down a question.

Use W04, My Food-Rule Questions and Nutrition Check, if a rule has led you to cut foods out. Ask what the rule is meant to do, what evidence supports it, and how you will still meet your needs. The task is to gain clarity, not to collect more food bans.

Frequently asked questions

Are carrots and beets unhealthy? No. Their exclusion describes this book’s Active Phase. It is not a universal nutrition judgment. Your health needs, portions, and overall pattern matter more. 2

Do whole grains stop fat loss? No evidence reviewed here supports that absolute claim. Whole grains can fit an eating plan aimed at health or weight management. You may need an alternative for an allergy or celiac disease, but that is a different question.

Can protein raise insulin? Yes. Some amino acids, the building blocks of protein, stimulate insulin release. That normal response does not make protein harmful. 5

Are all sweeteners the same? No. Compounds and doses differ, as do the foods they replace. Short-term hunger findings should not be turned into predictions of weight gain. 15, 16

Does a glucose spike prove a food caused weight gain? No. It describes a glucose response, not a measurement of fat gain. If you have diabetes, review glucose concerns with your care team rather than building sweeping food rules from one reading.

Related reading on NP FADY

• Article 1: What Thinsulin Gets Right, and What It Can’t Prove
• Article 3: Thinsulin’s Active Phase: The Plan and Its Limits
• Companion worksheets: W03 and W04 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. Food categories, traffic-light rules, and their stated exceptions.

2. World Health Organization. Carbohydrate intake for adults and children: WHO guideline. Geneva: WHO; July 17, 2023. ISBN 978-92-4-007359-3.

3. National Institute of Diabetes and Digestive and Kidney Diseases. Insulin Resistance & Prediabetes. Last reviewed March 2025.

4. Weiss M, Steiner DF, Philipson LH. Insulin Biosynthesis, Secretion, Structure, and Structure-Activity Relationships. In: Endotext. MDText.com; updated February 1, 2014.

5. 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

6. 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

7. Hall KD, Bemis T, Brychta R, et al. Calorie for Calorie, Dietary Fat Restriction Results in More Body Fat Loss than Carbohydrate Restriction in People with Obesity. Cell Metabolism. 2015;22(3):427–436. doi:10.1016/j.cmet.2015.07.021

8. Kidney Disease: Improving Global Outcomes. 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney International. 2024;105(4S):S117–S314.

9. World Health Organization. Healthy diet. Fact sheet. Updated January 26, 2026.

10. Linus Pauling Institute, Oregon State University. Glycemic Index and Glycemic Load. Micronutrient Information Center. Reviewed March 2016.

11. 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

12. Naude CE, Brand A, Schoonees A, Nguyen KA, Chaplin M, Volmink J. Low-carbohydrate versus balanced-carbohydrate diets for reducing weight and cardiovascular risk. Cochrane Database of Systematic Reviews. 2022;(1):CD013334. doi:10.1002/14651858.CD013334.pub2

13. 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

14. World Health Organization. Use of non-sugar sweeteners: WHO guideline. Geneva: WHO; May 15, 2023.

15. Pang MD, Kjølbæk L, Bastings JJAJ, et al. Effect of sweeteners and sweetness enhancers on weight management and gut microbiota composition in individuals with overweight or obesity: the SWEET study. Nature Metabolism. 2025;7(10):2083–2098. doi:10.1038/s42255-025-01381-z

16. Chakravartti SP, Jann K, Veit R, et al. Non-caloric sweetener effects on brain appetite regulation in individuals across varying body weights. Nature Metabolism. 2025;7:574–585. doi:10.1038/s42255-025-01227-8

---

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.

If you or someone you know is in crisis

• Call 911 or go to your nearest emergency room for any life-threatening emergency.
• 988 Suicide & Crisis Lifeline — call or text 988, available 24/7. En español: marque 988 y oprima 2. Veterans: 988 and press 1, or text 838255.
• Crisis Text Line — text HOME to 741741.
• The Trevor Project (crisis support for LGBTQ+ young people) — call 1-866-488-7386, or text START to 678-678.
• National Sexual Assault Hotline (RAINN) — call 1-800-656-HOPE (4673) or text HOPE to 64673; free, confidential, 24/7. Online chat at RAINN.org/hotline.
• National Domestic Violence Hotline — call 1-800-799-SAFE (7233) or text START to 88788; 24/7, help in 200+ languages. Online chat at TheHotline.org. If your phone or computer may be monitored, calling from a safer device is an option.
• Riverside County — Inland SoCal Crisis Helpline 951-686-HELP (4357), 24/7 (Inland SoCal United Way / 211+, in partnership with RUHS-BH); Community Access, Referral, Evaluation and Support (CARES) Line 800-499-3008, 24/7.
• San Bernardino County — Access Unit (Behavioral Health Helpline) 888-743-1478, 24/7; Mobile Crisis/CCRT 800-398-0018 (24/7, all ages) or text 909-420-0560. Arrowhead Regional Medical Center (ARMC) has a dedicated walk-in adolescent psychiatric ER (ages 13–17).
• Children under 13 — call 911 for immediate danger, contact your county's mobile crisis team (they respond to all ages), or go to the nearest pediatric emergency room.
• California Peer-Run Warm Line (non-crisis — someone to talk to) — call or text 1-855-600-WARM (9276); daytime and evening hours, not a 24/7 line.
• NP Fady (non-emergency) — for routine scheduling or questions, call (909) 707-6261. This line is not monitored for emergencies.