PDF Summary:How Not to Diet, by Michael Greger

If you’ve ever tried to lose weight, you’re probably aware of all the conflicting advice about what you should eat. Should you go on a low-carb diet, a low-fat one, or a liquid one? Eat one large portion in the morning, smaller portions throughout the day, or practice fasting?

In How Not to Diet, Michael Greger, physician and best-selling author of How Not to Die, adds a much-needed voice of clarity to the world of weight loss. He draws on extensive scientific research to explore the healthiest and most efficient way to lose weight and keep it off.

This guide explores Greger’s advice, covering:

• How eating processed foods and animal products leads to weight gain
• Why eating plant-based foods and legumes reduces the calories your body stores as fat
• What dietary changes will help you shed excess pounds and keep them off

Additionally, we’ll expand on each of Greger’s ideas with research, advice, and actionable ideas from other health practitioners and weight-loss specialists.

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• Protein into amino acids (4 calories per gram)

• Starches into simple sugars (4 calories per gram)

• Fats into fatty acids and glycerol (9 calories per gram)

Once all the food’s nutrients have been absorbed into your bloodstream, undigested matter travels to the large intestine.

5) Your large intestine separates the water from this matter and converts it to solid waste that moves through your colon to your rectum, where it waits until you have a bowel movement.

Negative Consequence #3: They Stimulate Inflammation in Your Body

According to Greger, processed foods and animal products stimulate inflammation within the body. He explains that, normally, inflammation is the body’s way of triggering the healing process whenever it gets hurt or sick. In this type of situation, the inflammation that occurs is short-term and targeted toward resolving a specific problem. For example, you stub your toe, and it looks and feels inflamed for a few hours until it heals.

However, processed foods and animal products contain high quantities of saturated fat and trans fat—substances that stimulate an inflammatory response that is long-term and unspecific. This means that the inflammation lingers in your whole body and, instead of healing you, it creates hormone imbalances that perpetuate many diseases such as heart disease, bowel disease, arthritis, and dementia. In addition to harming your health, these hormone imbalances contribute to weight gain because they raise your blood sugar levels, increase your appetite, and decrease your metabolism.

Chronic Inflammation Attacks Healthy Cells, Tissues, and Organs

Research confirms that processed foods and animal-derived products (particularly dairy and red meat) contribute to chronic inflammatory diseases and weight gain. Additionally, people who regularly eat these foods are at twice the risk of developing colorectal cancer, and they up their risk of mortality by 23%.

These foods cause inflammation, disease, and weight gain because they contain unnatural substances that your body classifies as threats to your immune system. To protect itself, it produces and sends out inflammatory cells to trap and neutralize these threats.

The more inflammatory foods you consume, the more inflammatory cells your body releases in response. These inflammatory cells build up and eventually start attacking healthy cells, tissues, and organs, resulting in diseases like diabetes, rheumatoid arthritis, and heart disease. In other words, your body’s attempts to protect your immune system actually weaken it. To compensate for this weakness, your body funnels even more resources toward protecting your immune system. As a result, it spends less energy digesting food—contributing to a decrease in metabolism and an increase in blood sugar levels and appetite.

Negative Consequence #4: They Increase the Number and Size of Fat Cells in Your Body

Greger argues that processed foods and animal products expose your body to chemicals that promote weight gain, such as organotins, BPA, and phthalates. He explains that, normally, the total number of fat cells in your body remains stable—when you gain or lose weight, these cells just enlarge or shrink. However, exposure to these chemicals creates hormonal imbalances that disrupt this stability. These imbalances activate the creation of new fat cells—by converting tissue stem cells into fat cells—and expand the size of existing fat cells.

While chemical pollutants get into our food via several sources in the processed food supply chain—such as plastic packaging—much of our food is contaminated before it’s packaged. This is because there are chemical pollutants both in the pesticides used to farm the crops that make our food and in the artificial additives used to make processed food more palatable.

Notably, Greger claims that 90% of chemical pollutant exposure comes from eating animal-derived foods (both organic and non-organic) such as meat, fish, and poultry—because, in addition to feeding these animals contaminated crops, livestock owners pump them full of artificial growth-enhancing hormones.

(Shortform note: Greger bases his claim that 90% of all chemical pollutant exposure comes from eating animal-derived foods on a study (1992-2022) that examined the correlation between organic pollutants and diabetes. The trial included 2,016 participants. More recent research from the Environmental Protection Agency clarifies that over 90% of exposure to a specific type of chemical (dioxin) does come from eating animal-derived foods.)

The Possible Effects of Chemical Pollutant Exposure and How to Avoid Them

Research on how organotins, BPA, and phthalates impact weight gain is still in the preliminary stages—the effects Greger discusses here are largely based on animal studies that haven’t yet been verified by human trials.

However, preliminary findings back up the theory that chemical pollutant exposure contributes to excess body weight. These studies speculate that these chemicals might interfere with your endocrine system. Because the endocrine system helps regulate metabolism and body weight, exposure to these chemicals may:

• Alter the rate of fat cell production versus destruction, favoring an increase in the number of fat cells you produce and store

• Shift energy balance, gut microbiota, and metabolism to favor calorie storage

• Modify hormonal control of appetite and satiety levels

There are approximately 1,000 different chemicals that may produce these effects. In addition to pesticides, packaging, and artificial additives and hormones, they’re present in everyday household items like food containers, toys, personal care products, and cleaning supplies. Since they’re present in such a wide range of sources, they contaminate our food, water, and air—making it impossible to avoid them entirely.

However, even though you can’t entirely avoid them, there are ways to reduce your exposure:

• Opt for organic produce and personal care products.

• Store food and beverages in stainless steel, aluminum, or glass containers.

• Avoid heating foods in plastic containers.

Part #2: Why a Plant-Based Diet Helps Maintain a Healthy Weight

Now that you understand why you crave high-calorie foods and how eating processed foods and animal products contributes to weight gain, let’s discuss why adopting a plant-based diet is the healthiest and most effective way to maintain a healthy weight.

A plant-based diet includes whole grains, legumes, fruits, and vegetables. It excludes processed foods and animal-derived products such as meat, fish, eggs, and dairy. Because it omits foods that are calorie-dense (high in fat, sugar or salt, and starch), it’s naturally high in nutritional value and low in calories. This means that you can eat as much of these foods as you want without having to restrict portion sizes—which makes this diet both healthy and easy to stick to.

(Shortform note: While nutritionists validate Greger’s claim that a plant-based diet is low enough in calories that you don’t have to restrict portion sizes, they do warn that it could lead to nutritional deficiencies and major health problems. This is because plant-based diets lack B12 and are low in heme iron, calcium, iodine, and DHA. Therefore, before adopting this diet, plan out how you’ll fulfill your nutritional needs by adding supplements or specific ingredients. This will help you maintain your weight and keep you in good health.)

Greger explains that plant-based foods have two positive effects that allow you to eat as much as you want and maintain a healthy weight:

• They reduce the number of calories your body stores as fat.
• They decrease your appetite and increase your metabolism.

Let’s explore these two positive effects in more detail.

Positive Effect #1: They Reduce the Number of Calories Your Body Stores as Fat

The first reason plant-based foods help maintain a healthy weight is that they contain plenty of fiber. According to Greger, fibrous foods reduce both the number of calories your body stores as fat and the number of calories you consume. Let’s explore these two effects in detail.

Fiber Reduces the Number of Calories Your Body Stores as Fat

According to Greger, fibrous foods reduce the number of calories your body stores as fat. This is because fibrous plants have tough outer layers that are difficult to digest. This means that your body can’t break these foods down and digest all of the calories before you excrete them.

Further, fibrous foods reduce the number of calories you extract from accompanying foods: As fiber passes through your body, it mixes with and encases other foods in your digestive tract. Because this casing is indigestible, it traps the calories in these other foods and prevents them from being extracted by your body before you excrete them.

For example, people who eat whole wheat pasta (high in fiber) with a cream sauce would excrete more calories from the cream sauce than those who pair the sauce with white pasta (low in fiber). This is because the fiber in the whole wheat pasta envelops the calories in the sauce and prevents them from being digested by your body.

The Difference Between Soluble Fiber and Insoluble Fiber

Research expands on how fibrous foods help prevent weight gain by explaining that most plants contain two types of fiber: soluble and insoluble. Though both types are indigestible, they help maintain a healthy weight in different ways.

Soluble fiber (two calories per gram) dissolves in bodily fluids to form a thick gelatinous substance that passes through your digestive tract. As Greger says, it encases other foods and prevents your body from extracting calories from them. Additionally, it encases fat and cholesterol—which means you excrete these substances instead of absorbing them. Sources of soluble fiber include apples, barley, beans, carrots, citrus fruits, oats, and peas.

Insoluble fiber (zero calories per gram) doesn’t dissolve in fluids. Instead, it absorbs fluids and sticks to other foods, forming bulkier stools that help keep you regular. Sources of insoluble fiber include beans, nuts, wheat bran, whole wheat flour, cauliflower, green beans, potatoes, and berries.

The recommended daily intake of fiber for people under the age of 50 is 25 grams for women and 38 grams for men, a quarter of which should come from soluble fiber.

Fiber Reduces the Number of Calories You Consume

Greger claims that fibrous foods also reduce the number of calories you consume in the first place. This is due to two reasons:

1) They require more chewing: This means they take longer to eat than processed foods. According to Greger, the more you chew, taste, and keep food in your mouth, the more satiated you feel, even if the food’s low in calories. This feeling satisfies your cravings for high-calorie foods and inhibits the tendency to reach for additional helpings.

(Shortform note: Multiple studies verify that chewing more leads to eating less during a particular meal. However, while Greger focuses on how chewing food during a meal reduces the amount you eat at that meal, studies reveal that chewing something tasteless, such as flavorless gum, before meals reduces appetite and prevents compulsive eating. This is because chewing tricks your brain into believing that you’re consuming real food and satiating your appetite. Because you believe that you’re already consuming food and filling up, you pay less attention to real food—which means you don’t crave foods that lead to compulsive eating.)

2) They require more effort to digest: As we’ve discussed, food remains in your stomach until the digestive process is complete. Greger explains that, since plant-based food takes a long time to digest, it makes you feel satiated for longer. This is both because your stomach is full for a longer period of time and because, during this time, it releases a steady supply of nutrients into your bloodstream.

(Shortform note: Fiber has long been known to satiate appetite and keep us full for longer. While previous research put this down solely to Greger’s two reasons—that fibrous foods take longer to chew and digest—recent studies reveal that there’s more going on beneath the surface. Digesting fiber releases an anti-appetite molecule (acetate) into the bloodstream, where it travels to and accumulates in the hypothalamus—a part of the brain that regulates hunger. Once there, it spurs chemical reactions that favor appetite suppression.)

Positive Effect #2: They Increase Your Metabolism and Decrease Your Appetite

The second reason plant-based foods help maintain a healthy weight is that, in addition to fiber and other nutritional content, fruits and vegetables are mostly full of water.

Greger explains that consuming foods with high water content fills you up more than just drinking water does. This is because water is trapped within the structure of these foods—which means your body requires more time and effort to separate the water from the food, and therefore burns more calories. (Recall: The longer it takes to digest food, the more calories you burn.) As a result, eating these foods naturally increases your metabolism and helps you burn calories and fat reserves more quickly.

Further, because water-rich foods take longer to digest, they sit in your stomach for longer, making you feel full for longer. Since water has zero calories, Greger emphasizes, these foods fill you up without adding to your calorie count.

(Shortform note: In addition to increasing your metabolism and filling you up, consuming water-rich foods provides two benefits over simply drinking water: It helps you absorb more nutrients and hydrates your body more effectively. Regular water intake is essential because the body is unable to store a reservoir of water. Since your body can’t store water, any water you drink quickly passes through your digestive tract—which means it doesn’t hydrate you for long. Along the way, it also flushes nutrients out of your body before you get a chance to digest them. However, consuming water-rich foods helps your body absorb water and any accompanying nutrients more slowly—thus providing hydration and nutrition more effectively.)

Part #3: How to Lose Weight on a Plant-Based Diet

Now that you understand why eating plant-based foods helps maintain a healthy weight, let’s discuss how to adapt this diet to accelerate weight loss. Greger suggests four dietary changes to achieve this:

1. Consume most of your calories early in the day.
2. Eat 30 grams of fiber each day.
3. Start every meal with water or foods with high water content.
4. Add anti-inflammatory ingredients to your food.

Let’s explore each of these four methods in detail.

Dietary Change #1: Consume Most of Your Calories Early in the Day

Aim to eat your largest meal in the morning, and your smallest meal in the evening. Greger explains that the amount of time and effort your body spends digesting food decreases during the day. This means that you burn more calories digesting food in the morning than you do in the evening. Therefore, eating more food earlier in the day reduces the overall number of calories your body stores as fat throughout the day.

Example: Consuming Food Early Decreases the Number of Calories Your Body Stores

Since metabolic rates hinge on multiple factors, Greger doesn’t define exactly how many more calories you burn in the morning. However, we’ll provide a hypothetical example to illustrate how this principle works.

Let’s say that, during digestion, you burn half the calories of the food you eat in the morning compared to a quarter of the calories of the food you eat in the evening. If you consume 1,000 calories during the day, the number of calories you burn or store as fat would differ depending on when you ate your largest meal.

If you consumed 750 calories in the morning and 250 calories in the evening, you would burn 437.5 calories and store 562.5 as fat: (750 ÷ 2) + (250 ÷ 4) = 437.5 calories burned. 1,000 - 437.5 = 562.5 calories stored.

However, if you consumed 250 calories in the morning and 750 calories in the evening, you would burn 312.5 calories and store 687.5 as fat: (250 ÷ 2) + (750 ÷ 4) = 312.5 calories burned. 1,000 - 312.5 = 687.5 calories stored.

(Shortform note: While research backs up the claim that early meals contribute to weight loss, it offers a different theory to explain it. Studies reveal that people who eat most of their daily calories in the morning don’t burn more calories than those who eat more in the evening. However, people who eat a large breakfast do report feeling less hungry during the day and don’t feel the urge to snack between meals. Therefore, because consuming a large breakfast helps keep calorie intake in check, it can contribute to weight loss.)

Dietary Change #2: Eat 30 Grams of Fiber Each Day

As we’ve previously discussed, fiber reduces both your appetite and the number of calories your body digests. However, Greger argues, 97% of Americans fall far short of the recommended minimum daily amount. (Shortform note: Recall that the recommended daily intake for people under the age of 50 is 25 grams for women and 38 grams for men.) He suggests that you can easily up your fiber intake by replacing white foods with whole grain equivalents (for example, replacing processed white pasta with whole wheat pasta) and adding root vegetables and legumes such as chickpeas, lentils, and black beans to your diet.

(Shortform note: Research validates Greger’s claim that most Americans fall short of the recommended minimum daily amount of fiber. However, while there’s no disputing that consuming more fiber helps you lose or maintain weight, proceed with caution: Gradually introduce fibrous foods into your diet. Research reveals that dramatically increasing your daily intake can cause adverse side effects. These effects include bloating, abdominal pain, flatulence, diarrhea, constipation, and temporary weight gain. It can also create complications for people with Crohn’s disease or diabetes.)

Dietary Change #3: Start Every Meal With Water or Foods With High Water Content

Greger suggests that, in addition to staying hydrated throughout the day, you should drink water before each meal. This is because any water you drink sits in your stomach for a short while, during which time it makes you feel full. Additionally, eat water-rich foods such as fruits, vegetables, soups, or salads as a starter. The water you drink or consume will satiate you and reduce your appetite for the main meal. As a result, you’ll consume fewer calories overall.

How Keeping Hydrated Contributes to Weight Loss

We’ve already explained why consuming water-rich foods helps you lose or maintain weight—because it fills you up, increases your metabolism, helps you absorb more nutrients, and hydrates your body. But, we haven’t yet explored how keeping hydrated helps you lose weight.

Though many studies show a positive correlation between increased water consumption and weight loss, researchers are still unsure about why it’s so effective. They offer five possible reasons:

1) It suppresses appetite: As Greger says, liquids take up space in the stomach, creating a feeling of fullness that reduces appetite. The following list breaks down how long different types of liquids remain in your stomach:

• Plain water: 10 to 20 minutes

• Simple liquids (juice, tea, and soda): 20 to 40 minutes

• Complex liquids (smoothies and protein shakes): 40 to 60 minutes

2) It curbs unnecessary calorie consumption: People often confuse feeling thirsty with feeling hungry, which leads them to consume more food than they need.

3) It helps you burn more calories: The body expends more energy heating up cold water in preparation for digestion.

4) It removes waste from your body: Water helps filter toxins, prevents constipation, and reduces bloating and swelling—factors that can add extra pounds to your weight.

5) It helps metabolize fat: The body needs water to effectively metabolize fats and carbohydrates in the digestive tract as well as the fats it has stored.

Dietary Change #4: Add Anti-Inflammatory Ingredients to Your Food

Gregers suggests that you drink three cups of green tea each day, and add the following ingredients to your food: turmeric, ginger, garlic, nutritional yeast, vinegar, black cumin, and cayenne pepper. These ingredients are high in anti-inflammatory properties. (Recall: Inflammation creates hormone imbalances that increase blood sugar levels and appetite.) This means that consuming anti-inflammatory ingredients prevents blood sugar spikes, regulates appetite, and boosts metabolism.

Possible Side Effects of Consuming Anti-Inflammatory Ingredients

Research in this area isn’t definitive—while ongoing studies suggest that consuming these ingredients might prevent blood sugar spikes, regulate appetite, and boost metabolism, they also reveal numerous possible side effects to consider before adding them to your diet:

Green tea:

• People with severe caffeine sensitivities may experience insomnia, anxiety, irritability, nausea, or an upset stomach.

• Consuming the tea alongside stimulant drugs may increase blood pressure and heart rate.

Turmeric:

• It stimulates the production of gastric acid, which can lead to an upset stomach.

• It thins the blood—making it unsafe for pregnant women or people who take blood-thinning drugs.

Ginger:

• Large doses (more than five grams a day) may cause gas, heartburn, an upset stomach, or mouth irritation.

• It might be unsafe for people who take blood-thinning drugs or medication for diabetes or high blood pressure.

Garlic:

• Excess consumption can trigger migraines and cause dizziness, nausea, vomiting, heartburn, diarrhea, gastroesophageal reflux disease, swelling in the kidneys, and liver toxicity.

• It may lead to bad breath, excess sweating, vaginal yeast infections, and skin irritations such as eczema or rashes.

• It might be unsafe for people who take blood-thinning drugs or medication for high blood pressure.

Nutritional yeast:

• It can cause gas or an upset stomach.

• Possible allergic reactions include hives and asthma.

• It might be unsafe for people with Crohn’s disease; elevated yeast antibody counts; or an autoimmune disease such as rheumatoid arthritis, lupus, or multiple sclerosis.

Vinegar:

• Because it’s highly acidic, it can cause acid burns and injury to the digestive tract (the throat, esophagus, and stomach) resulting in ulcers, gastritis, vitamin deficiencies, and an increased risk of developing cancer of the upper gastrointestinal tract.

• It damages the liver and kidneys, irritates the central nervous system, and may decrease potassium levels and bone density.

• It can cause hypoglycemia, creating symptoms such as anxiety or dizziness.

• It may weaken tooth enamel, leading to cavities and other dental problems.

• Due to its tyramine levels, it may cause high blood pressure, joint pain, urticaria, IBS, and headaches.

• It might be unsafe for people who take blood-thinning drugs, laxatives, diuretics, or medications for diabetes or heart disease.

Black cumin:

• It may cause nausea and bloating.

• Due to limited research on its side effects, women who are pregnant or breastfeeding should only use small amounts for flavoring food.

• It might be unsafe for people with kidney problems or those who take blood-thinning drugs or beta-blockers.

Cayenne pepper:

• In addition to causing irritability to the throat, mouth, and nose, it may lead to heartburn, stomach disorders, nausea or vomiting, and bronchitis.

• It aggravates IBS and gastroesophageal reflux disease symptoms.

• Possible allergic reactions include eczema, swelling, coughing, urticaria, and conjunctivitis.

• It might be unsafe for people who take blood-thinning drugs, ACE inhibitors, and antacids.