- WW (Weight Watchers)
- Meal-Replacement Plans
- Volumetrics
- Blood Type Diet
- Alkaline Diet
- Juice Cleanses and Detox Diets
- Intermittent Fasting
No. 74WW (Weight Watchers)
Jean Nidetch, a homemaker in Queens, New York, began meeting with friends at home to talk about weight, and in 1963 she founded Weight Watchers. Not bad for a kitchen-table chat. The program gives each food a number of points, gives each member a daily budget, and adds weigh-ins and group meetings. The company renamed itself WW in 2018, and the points formula has changed many times, so yesterday's math may not add up.
Strengths
- One of the best-studied commercial programs. Trials have found modest weight loss, often more than people manage with standard advice from their doctor.
- Group meetings and coaches give encouragement and accountability. Someone is going to ask how your week went.
- No food is forbidden, so it can fit family meals, holidays and cultural dishes. Many vegetables and fruits count as zero points in recent versions.
Watch out for
- Points are calorie counting in a nicer outfit. Like most diets, it works by helping you eat less, and long-term results depend on sticking with it. Many people regain weight after they stop.
- Older point systems rewarded low fat, which steered members toward processed "diet" foods (including branded snacks) instead of traditional fats like butter, olive oil and nuts.
- A food can be low in points and still be ultra-processed. The points don't read the ingredient list; you have to.
- The company now also offers prescription weight-loss medications through a telehealth service. These are drugs with real side effects, including nausea and muscle loss, and the weight tends to return when they stop.
Eating well within it
- Spend points on whole foods (eggs, fish, beans, plain yogurt, vegetables, fruit) rather than bars and low-fat snacks.
- Save some of your budget for olive oil, butter or nuts. A little real fat keeps meals satisfying, and keeps you out of the pantry later.
- Use the group for recipes and support.
Possible supplement needs
Usually none if meals are varied. Vitamin D if sun exposure is low.
Who should be careful
People with a history of eating disorders, since tracking and weigh-ins can stir up old patterns. People with diabetes: their medicines may need lowering as they lose weight.
No. 75Meal-Replacement Plans
These plans replace some or all of your meals with shakes, bars and prepackaged meals. Dinner, meet the blender. SlimFast, sold since the 1970s, made famous the idea of a shake for breakfast, a shake for lunch and a sensible dinner. Optavia, Nutrisystem and Jenny Craig sell boxed meals and snacks, often with coaching. Some plans are very low in calories.
Strengths
- Structure and built-in portion control take away the guesswork. Studies find meal replacements often lead to more weight loss than a standard diet, at least in the first year.
- Medically supervised liquid-diet programs have done well in research. In the UK DiRECT trial, many people with type 2 diabetes went into remission.
- Convenient for busy people: no chopping, no recipe, no dishes.
Watch out for
- Most products are ultra-processed: protein isolates, added sugar or sweeteners, gums, seed oils and added synthetic vitamins. The label reads like a chemistry quiz.
- They don't teach you to shop or cook, so weight often returns when you stop. The weight comes off because you eat less, and results depend on what you do afterward.
- Costly over time. Those boxes add up, and so do the bills.
- Very-low-calorie plans (usually under 800 calories a day) need medical supervision. Risks include gallstones, dizziness, hair loss and low electrolytes.
Eating well within it
- Use a replacement for one meal at most, and build the others from whole foods.
- Read labels and choose products with short ingredient lists and little added sugar. Better yet, make your own shake with plain yogurt or whole milk, berries and nut butter.
- Before you stop, copy the boxed meals' portion sizes with home cooking. Let the box teach you, then retire it.
Possible supplement needs
Products are usually fortified, so extra vitamins are seldom needed. Fiber may be low on shake-heavy plans.
Who should be careful
Pregnant or breastfeeding women, teens, and people with eating disorders. People with diabetes, heart or kidney disease, or on regular medicines should know that rapid weight loss changes how medicines act.
No. 76Volumetrics
Volumetrics was developed by Dr. Barbara Rolls, a nutrition scientist at Penn State. Its core idea is energy density: the number of calories in each bite. Foods high in water and fiber, such as broth-based soups, vegetables, salads and fruit, have few calories for their size, so you can eat a full plate and still eat less. It's the rare diet that tells you to pile it on. Foods are sorted into four groups, from "eat freely" to "eat sparingly."
Strengths
- Based on decades of research in Dr. Rolls's lab. Her studies found that people tend to eat a fairly steady amount of food, and that starting a meal with soup or salad led to fewer calories overall.
- No food is banned, and you are not left hungry, two things most diets can't promise.
- Steers you toward vegetables, fruit, beans and whole grains.
Watch out for
- It is still a calorie-reduction diet, just a roomier one. Long-term results depend on sticking with it.
- It can make nourishing foods look bad. Nuts, olive oil, avocado, cheese and butter are energy-dense, yet they are filling and healthy in sensible amounts.
- Low-fat or "light" processed products may score well even though they are ultra-processed. "Light" describes the calories, not the ingredient list.
- Vitamins A, D, E and K need some fat to be absorbed, so a salad with no dressing is a missed chance.
Eating well within it
- Start meals with a broth-based vegetable soup or a large salad dressed with olive oil.
- Bulk up favorite dishes: add extra vegetables to stews, pasta sauce, eggs and ground meat.
- Keep a measured portion of traditional fats at each meal rather than cutting them out.
Possible supplement needs
Usually none on a varied plan.
Who should be careful
People who are underweight, older adults with small appetites, children, and anyone recovering from illness, since they often need energy-dense food.
No. 77Blood Type Diet
Dr. Peter D'Adamo, a naturopathic physician, introduced this diet in his 1996 book Eat Right 4 Your Type. He taught that each ABO blood type arose at a different point in human history and reacts differently to proteins in food called lectins, so each type should eat differently. Type O is told to eat plenty of meat and limit wheat and dairy, type A to eat a mostly vegetarian diet, type B a varied diet that includes dairy, and type AB a mix of A and B. It's a tidy system, which is a big part of its charm.
Strengths
- Every version cuts back on processed food, and most encourage vegetables, so many people feel better on it. That part works for every blood type.
- It encourages you to notice how foods affect you.
Watch out for
- There is no good evidence that blood type should guide your diet. A 2013 review of the research found no studies supporting it. Not weak evidence: none.
- A 2014 study from the University of Toronto found that some of the plans were linked with better heart and blood sugar markers, but the benefits appeared whether or not people had the matching blood type. The food helped; the blood type was along for the ride.
- Strict versions cut out whole food groups. Type O plans without dairy or grains can run low in calcium and fiber; type A plans can run low in protein, iron and vitamin B12.
Eating well within it
- Keep your plan's whole-food parts: vegetables, fruit, beans, fish and less processed food.
- Don't drop a whole food group because of your blood type. If you do avoid one, replace what it gives you (for example, calcium from sardines with bones, leafy greens or yogurt).
Possible supplement needs
It depends on what you cut out: calcium and vitamin D if you avoid dairy, vitamin B12 if you eat little or no animal food.
Who should be careful
People with diabetes, heart or kidney disease, pregnant women and children, whose food needs depend on their health, not their blood type.
No. 78Alkaline Diet
Supporters say meat, grains, sugar, coffee and alcohol make the body "acidic" and cause illness, and that eating "alkaline" foods, mainly vegetables, fruit, nuts and legumes, restores balance. The idea grew from an early-1900s theory called the acid-ash hypothesis and spread through popular books. Foods are ranked by the effect they leave after digestion, not by taste, so lemons count as alkaline. Yes, lemons. Chemistry loves a twist.
Strengths
- The food list is mostly vegetables, fruit, nuts, seeds and legumes, with little processed food, sugar or alcohol. That, not pH, is its real benefit.
- Rich in potassium, magnesium and fiber, which keep blood pressure down.
Watch out for
- Food does not change your blood pH. Your lungs and kidneys keep blood within a narrow range (about 7.35 to 7.45) no matter what you eat. A shift outside it is a medical emergency, not a salad problem.
- Urine pH does change with diet, and that is what home test strips measure. It shows your kidneys at work, not your body's pH.
- Studies have not shown that an alkaline diet protects bones or works against cancer.
- Strict versions limit meat, fish, eggs, dairy and grains, which can leave you short on protein, vitamin B12 and calcium.
- Alkaline water is costly and unnecessary, and drinking baking soda as a remedy can be dangerous. Baking soda belongs in the muffins.
Eating well within it
- Keep vegetables and fruit at the center of most meals.
- Include eggs, fish, meat or dairy in moderate portions next to plenty of vegetables, rather than cutting them out.
- Skip the test strips and alkaline water, and spend the money on vegetables.
Possible supplement needs
Vitamin B12 if you eat little or no animal food; calcium and vitamin D if you cut out dairy.
Who should be careful
Kidney disease is the exception where the acid load of the diet does matter. But many people with kidney disease must limit potassium, so a high-potassium diet can be dangerous for them.
No. 79Juice Cleanses and Detox Diets
These plans replace food with liquids for days or longer, promising to flush out toxins. The best known is the Master Cleanse, created by Stanley Burroughs in the 1940s: a lemonade of lemon juice, maple syrup, cayenne pepper and water, often with salt-water flushes and laxative tea. Others include juice fasts and "detox" teas, each with a label promising more than the bottle can deliver.
Strengths
- A short break from alcohol, fast food and snacking.
- Fresh juices supply some vitamins, potassium and plant compounds.
- Some people use it to start healthier habits.
Watch out for
- Your liver and kidneys remove waste all day, every day, free of charge. No good studies show that juice cleanses remove toxins or improve this work.
- The quick weight loss is mostly water and stored carbohydrate, and it comes right back when you eat again.
- Juice is low in protein and fiber and often high in sugar. This can bring blood sugar swings, hunger, shakiness and irritability: hangry, bottled.
- Large amounts of green juice (spinach, chard, beet greens) are high in oxalate. Doctors have reported kidney injury from oxalate in people on green-juice cleanses.
- Detox teas often contain senna or other laxatives, which can cause cramping, diarrhea, dehydration and loss of potassium. That's not a detox; that's a bad afternoon.
Eating well within it
- Try a whole-food reset instead: a few days of vegetables, fruit, beans, eggs, fish and water, with no alcohol.
- Blend instead of juicing to keep the fiber, and add yogurt or nut butter for protein.
- If you love juice, have a small glass with a meal and rotate your greens.
Possible supplement needs
None needed. Skip laxative and "detox" teas.
Who should be careful
People who are pregnant or breastfeeding, children and teens, and anyone with diabetes, kidney disease, kidney stones or an eating disorder should not do a cleanse. Anyone on regular medicines should know that some juices (grapefruit, large amounts of leafy greens) affect how medicines work.
No. 80Intermittent Fasting
Intermittent fasting sets times for eating, rather than rules about foods: it cares about when, not what. Common patterns are 16:8 (eating within an 8-hour window), 5:2 (eating normally five days a week and about 500 to 600 calories on two), alternate-day fasting, and one meal a day. British doctor and journalist Dr. Michael Mosley popularized 5:2 in The Fast Diet, and Canadian kidney specialist Dr. Jason Fung promoted fasting in The Obesity Code. Fasting itself is far older, part of many faiths through Ramadan, Lent, Yom Kippur and more; the diet books are the newcomers.
Strengths
- Simple: no special foods and fewer meals to plan. Some find it easier than counting calories.
- Many people lose weight, and some see better blood sugar, insulin and blood pressure.
Watch out for
- Trials comparing fasting with ordinary daily calorie cutting usually find similar results, including a year-long trial in China published in 2022. The benefit seems to come mainly from eating less, and depends on sticking with it. The clock isn't magic.
- The eating window is not a free-for-all. Ultra-processed food eaten in eight hours is still ultra-processed; a doughnut doesn't turn into health food at noon.
- Hunger, headaches and irritability are common at first.
- One meal a day can make it hard to get enough protein, fiber and nutrients, especially for older adults protecting their muscle.
Eating well within it
- Break your fast with protein, vegetables and a traditional fat rather than sweets or white bread.
- Start gently with a 12-hour overnight fast (you'll sleep through much of it), and lengthen it only if you feel well.
Possible supplement needs
Usually none. On longer fasts, add electrolytes (salt, potassium and magnesium).
Who should be careful
People who are pregnant or breastfeeding, underweight, under 18, or have a history of eating disorders should not fast this way. People with type 1 diabetes, or who take insulin, sulfonylureas or SGLT2 inhibitors, should fast only under their doctor's care because of the risk of dangerously low blood sugar or ketoacidosis.
In depth
What happens when you fast
- 0 to about 4 hours after a meal: the body is digesting and running on the food just eaten. Insulin is up, and the body stores energy.
- About 4 to 16 hours: insulin falls. The liver releases stored sugar (glycogen) to keep blood sugar steady, and the body begins to burn more fat.
- About 16 to 48 hours: liver glycogen runs low. The body breaks down fat for fuel, and the liver turns some fat into ketones, an alternative fuel the brain can use. Growth hormone rises, which helps protect muscle.
- Beyond 2 to 3 days: ketones are high, hunger often settles, and the body relies mainly on fat. This is where the risks of fasting rise too (Who should not fast, and how to fast safely).
The timing varies with the person, their last meal and how active they are.
Fasting styles
| Style | How it works | Notes |
|---|---|---|
| Time-restricted eating, 12:12 | Eat within 12 hours, fast 12 (for example 7 a.m. to 7 p.m.) | A gentle start: no late-night eating |
| 16:8 | Eat within 8 hours, fast 16 (for example noon to 8 p.m.) | The most popular style; usually means skipping breakfast |
| 5:2 | Eat normally five days; about 500–600 calories on two non-consecutive days | Popularized by Dr. Michael Mosley |
| Alternate-day | Alternate normal days with fasting or very low-calorie days | Harder to keep up |
| One meal a day (OMAD) | A single meal within about an hour | Hard to meet protein and nutrient needs |
| Extended fast | 24 hours to several days, water or broth only | Rare and supervised; see Who should not fast, and how to fast safely |
Essential Fasting (2020). Jordan Rubin (see Before the Diets: Whole Food and the Gut) and Dr. Josh Axe (see Ketogenic Diet) present a range of fasts: intermittent fasting and time-restricted eating, 16:8, a "warrior" style with one main evening meal, alternate-day, 5:2, partial fasts such as vegetable-and-fruit fasts, and short water fasts. They pair fasting with whole-food meals, broth, and recipes for breaking a fast. The book also includes a spiritual side of fasting, which a coach can leave to the client's own beliefs.
Choosing a style. The best fast is the one a client can do safely and keep doing. Most people start with 12:12, then 14:10, then 16:8 if it suits them.
Dr. Jason Fung: insulin and fasting
Dr. Jason Fung is a kidney specialist in Toronto. In The Obesity Code (2016) and The Complete Guide to Fasting (2016, with Jimmy Moore), he teaches:
- Insulin drives fat storage. Eating often, especially sugar and refined carbohydrates, keeps insulin high, and high insulin tells the body to store fat. Over time the body becomes resistant to insulin, and insulin climbs higher.
- Weight is hormonal, not just calories. "Eat less, move more" fails for many people, he argues, because the body lowers its metabolism when calories drop while insulin stays high.
- Fasting lowers insulin. Long gaps between meals, and occasional longer fasts, let insulin fall so the body can use stored fat. He has used fasting with many patients with type 2 diabetes, under medical supervision.
Where others disagree. In a 2021 NIH study, Dr. Kevin Hall (see Before the Diets: Whole Food and the Gut) found that people ate about 700 fewer calories a day on a low-fat, high-carbohydrate diet than on a low-carbohydrate diet, even though insulin was higher on the low-fat diet; that does not fit a purely insulin-driven model. Controlled trials of time-restricted eating, such as a 2022 one-year trial in the New England Journal of Medicine, found that adding an 8-hour eating window to a reduced-calorie diet brought no more weight loss than the reduced-calorie diet alone. A fair summary: fasting is a useful way for many people to eat less and to improve blood sugar, but it is not magic, and it works best with whole-food meals.
Autophagy: what is known
Autophagy ("self-eating") is the process by which cells break down and recycle worn-out parts. Dr. Yoshinori Ohsumi won the 2016 Nobel Prize in Physiology or Medicine for discovering how it works, in yeast.
- What is known: fasting and nutrient shortage switch on autophagy in cells and in animals.
- What is not known: there is no reliable test of autophagy in a living person, and no known number of hours at which it "switches on" in humans. In the video, Dr. Fung says the same.
- How to teach it: "Fasting appears to support the body's own cell clean-up. We don't know exactly when or how much in people." Avoid promises such as "autophagy starts at 16 hours" or "fasting kills cancer cells."
Who should not fast, and how to fast safely
Who should not fast:
- Pregnant or breastfeeding women
- Children and teenagers under 18
- Anyone with a current or past eating disorder
- Anyone underweight, frail or older and losing weight
- Type 1 diabetes
- Anyone on insulin, sulfonylureas (such as glipizide or glyburide) or other medicines that lower blood sugar (risk of dangerously low blood sugar)
- Anyone on an SGLT2 inhibitor such as Jardiance, Farxiga or Invokana (risk of ketoacidosis even with normal blood sugar)
- Anyone on blood pressure pills or water pills (risk of dizziness and electrolyte problems), or medicines that must be taken with food
- Gout, kidney disease, heart disease, or a history of gallstones
Refeeding syndrome. After a long fast, especially in someone thin or poorly nourished, eating a large meal can cause a dangerous shift of potassium, phosphate and magnesium. Clinicians consider someone at high risk after more than about 5 to 10 days of eating little or nothing. This is why fasts longer than about three days happen only under medical supervision.
Fasting well:
- Start small: 12:12, then lengthen the window over weeks.
- Drink water, and plain tea or black coffee if tolerated.
- Electrolytes: headaches, dizziness and cramps during fasting usually come from losing sodium and water. A pinch of unrefined salt in water helps many healthy people (see From A to Zinc for cautions).
- Break the fast gently: a modest whole-food meal with protein, such as broth and eggs, not a feast of sweets.
- Eat enough on eating days: fasting is not an excuse to under-eat protein.
- Stop if the client feels faint, confused, has a racing heart, or feels unwell beyond mild hunger.
Women and fasting. Some women find long or frequent fasts upset their sleep or menstrual cycle. Gentler windows (12 to 14 hours), and fasting less around the period, often work better.
Safety notes
- Medications: diabetes medications (especially insulin, sulfonylureas and SGLT2 inhibitors), blood pressure medication and water pills change how a fast goes: doses often have to come down first, and only the prescriber changes them. Some medications must be taken with food.
- Who should not fast: see Who should not fast, and how to fast safely.
- Fasts longer than about 3 days happen only under medical supervision (refeeding syndrome).
- Eating disorders: fasting can trigger a relapse. Do not suggest fasting to anyone with a current or past eating disorder.
- Warning signs: faintness, confusion, a racing or irregular heartbeat, severe weakness or vomiting mean the client eats and calls their doctor.
- Electrolytes: clients with kidney disease, heart failure or high blood pressure keep to the salt and potassium limits they have been given.