Sharing my thoughts and the most interesting insights from How Not to Diet by Michael Gregor, MD


In the introduction of How Not to Diet, author Michael Gregor, MD describes this book as forty books in one, adding that it is the compact version. An apt description of its content and although the book is only 570 pages long, it took me months to read through all of it. Six months if we’re being specific. It’s a complex read packed with an enormous amount of research focused content and while he writes in a way that is easily digestible, I found (much like the way he suggests eating) that small bites taken in slowly, was the way to read it.


In How Not to Diet, Dr Greger has put together a compact history of food, diet industry and thousands of studies done on weight loss and diets. He details just about every single diet intervention from weight loss surgeries and diet pills, all the way to fasting, keto and plant-based diets. The book is not about aesthetics or the “perfect body”, it is focused on health and discusses weight loss from a medical and scientific view.


He emphasizes that he donates all earnings from his books to charity. His motivation, he says, is not financial but to provide the most accurate information. His goal with this book was to come up with the best diet by looking though all the research on diets and weight loss he could find, and selecting those that worked and were not harmful.


The first part of the book is heavily focused on diet pills, weight loss surgeries and extreme measures to lose weight. I found the enormous amount of studies and extreme measures to be quite depressing – sure you can lose weight, just sleep in a bed with a slight angle ?.


He ends the book by sharing his 21 tweaks to accelerating weight loss. These tweaks are based on his extensive research throughout the book. When I started reading the book, I intended on sharing his 21 tweaks, assuming them to be the most useful or interesting parts of the book. After I had a change of heart because some of those tweaks were the biggest issues I had with the book, and things I’d rather not promote.


Before sharing my “issues”, I must clarify that I am not a doctor, nutritionist, dietician, or scientist. My opinion is based on my own experience, thoughts and spending years interested in and writing about health, wellness and nutrition and consuming heaps of content around these subjects. You may justifiably prefer to listen to the person whose name ends in MD and who hired 9 fact checkers to go through the book, (who I may add, do offer some valuable and useful insight). However I think that when writing a book review I must give my honest opinion on it, which is weighted from a different, more everyday perspective.


My issue with his 21 tweaks was that in a previous chapter he discussed what makes the perfect diet and he listed 3 criteria – it needs to be effective, sustainable, and safe. He gives the example of water fasts which are 100 percent effective, but (IMPORTANTLY) also 100 percent fatal if you stick with it. I was left wondering how sustainable and safe some of his tips are i.e. adding very specific amounts of things to your daily diet (like having 2 teaspoons of apple cider vinegar daily and ½ teaspoon of cumin with your lunch and dinner).


The tweak I took the most issue with was his suggestion to weigh yourself twice a day. The number, he got from a study, which showed twice a day led to more weight loss than once a day. The scale can be triggering for many people and even if it isn’t yet the constant weighing can lead to becoming obsessed with a number – and letting that number dictate how you feel about yourself and what you eat. Weight, we know fluctuates throughout the day depending on how many times you have gone to the bathroom, water retention and, for women, where you are in your cycle.  I would think weekly weigh-ins would give one a more accurate picture and cause less stress. I appreciate that he backs everything up with science, however life does not occur in a bubble and safety should also include mental health. I cannot see how it would be good for one’s mental health to do a twice daily weigh in, in fact in most cases I do see how that could be harmful. I think a lot of the science fails to account for the mental aspect of weight and weight loss and the human factor.


Despite those misgivings, I really enjoyed his chapters on nutrition and the gut and I found the middle parts of his book really interesting. Overall it was a book I learnt a lot from and I think it holds value.


I appreciated his focus on health, not aesthetics, even if I found his approach to food to veer on the extreme restrictive path and found it exhausting. I think there is a way to eat healthy nutritious meals that truly taste good. I also believe that there is a balance between taking into account the nutrition of your food but also getting enjoyment from it and not painstakingly counting nutrients of everything you eat. Does every meal need to be optimised for nutrition? His BROL morning bowl may be packed with nutrition, but I’d prefer having barley, rice, oats and lentils separately with maybe some roasted vegetables drizzled in olive oil, not sautéed in water as per his preference.


So, instead of sharing his tweaks, I’m sharing a few things I bookmarked. They’re a drop in the ocean of the insights this book offers but are the things that stuck with me.


On weight loss supplements

Weight loss supplements are not required to be approved for safety by the FDA and because of this most are not. There is no guarantee that what is listed on the label is what you get inside. In fact, FDA inspectors have found that 70% of supplement manufacturers violated the Good Manufacturing Practices, which are the minimum quality standards and include things like basic sanitation and ingredient identification.


Even more frightening is that weight loss supplements often contain drugs. In a sample of 160 “100% natural” weight loss supplements more than half were tainted with drugs, ranging from anti-depressants to erectile dysfunction meds. And perhaps the most terrifying is that some have been tentatively linked to sudden death. They may make you lose weight, but they can also kill you.


On advertising in the food Industry

Unhealthy foods are advertised more than healthy foods because that is where the money is. Fruits and vegetables are perishable, and shareholders would rather a cake that can last for weeks on the shelf. Furthermore, real food does not have brand names. A broccoli is a broccoli no matter where it comes from. He shared a 1965 quote from a Kellogg’s ad executive who said “our primary goal is to sell products to children, not educate them. If you sell a woman a product and she goes into a store and can’t find it, she’ll forget about it. But when you sell a kid on your product, if he can’t get it, he will throw himself on the floor, stamp his feet and cry. You can’t get a reaction like that out of an adult”


On inflammation

According to Dr Gregor one of the most important medical discoveries in recent years was realising that inflammation plays a role in many chronic diseases. Throughout most of human history, inflammation was seen as a good thing. Inflammation is your body’s natural reaction to tissue damage or irritation, like when you bump your toe, and it gets red and painful, it’s what triggers the healing process. That is acute inflammation – it is short-term, localised and a specific response to an injury/infection. Where inflammation becomes harmful is when it is chronic, also known as metabolic inflammation. This inflammation is persistent, systematic, non-specific and appears to make us sick. He says that in addition to pollution, stress, smoking and toxic chemicals, the primary driver of meta inflammation is what we put into our bodies – food. The best anti-inflammatory foods to eat are turmeric, ginger, green or black tea and foods high in fibre (fruits, vegetables, legumes) and flavones (herbs, vegetables, and fruits). They also, he added, help control one’s appetite.



BPA is one of the most widely used chemicals worldwide. Exposure at all life stages tends to correlate with weight gain. He recommends choosing beans and tomato products that are in jars not cans unless you can find them in BPA free cans. Look out for recycling codes 3 and 7 on plastics which indicate items more likely to have higher levels of BPA in them.


On Organic

I appreciated his take on organic and his acknowledgement that if you look at the profiles of organic shoppers, you’ll find that they are more educated and better off financially. They also tend to exercise and eat more plants, so looking at organic vs non organic from a weight perspective won’t give you accurate results. He also pointed out that organic doesn’t mean healthy – you get plenty organic processed foods and sweets. His takeaway was that while he tries to eat organic wherever possible, he doesn’t let that get in the way of eating as many fruits and vegetables as possible, regardless of how they’re grown.


On eating water rich foods

Eating water rich foods is more effective at reducing food intake than having water alongside food. This is because when you have water alone your stomach strains it right out. When water is part of the food, it forms one mass that slowly empties from you stomach over time, keeping you satiated for longer.


On the Microbiome

This was the section I found most interesting.

The human colon has been considered the most bio-dense ecosystem in the world – there is more life concentrated in our colon than anywhere else on earth. 75% of you stool is pure bacteria.


More bacteria live and work in one linear centimetre of your lower colon than all the humans who’ve ever lived

– Neil de Grasse Tyson


One of the most interesting things I learnt about the microbiome is that even though there are so many different types of gut bacteria, people tend to split into just one of two groups. Those who grow mostly Bacteroides species and those that grow mostly Prevotella species. He goes on to explain that your enterotype does not depend on where you live, your gender or your age. What matters is what you eat.


Researchers looked into hundreds of different food factors and discovered that Bacteroides and Prevotella are opposites. The prevalence of Bacteroides is correlated to the consumption of components found in animal food, such as animal fat, cholesterol, and animal protein. Prevotella are linked to components found almost exclusively in plants – they’re fibre-feeders and pump out more short-chain fatty acids. This means that the biggest factor is whether you follow an animal-based diet or plant-based diet.


Researchers also discovered that by changing what you eat you are able to change your enterotype. Within 24 hours of switching diets there is already a huge difference in the bacteria in your gut – it changes as soon as food hits your gut and adjusts to what you eat. He says that plant-based is the healthiest diet as it yields more protective short-chain fatty acids but says its benefits don’t have to be all or nothing. A Mediterranean diet that is heavier on plants than meat, eggs or dairy yields a comparative level of short-chain fatty acids to vegans.


Having a greater diversity of gut flora is also associated with less body fat and less weight gain over time. Traditional societies tend to have more diverse gut flora (the Yonomami tribe in the Amazon jungle who previously had no contact with the modern world had the richest microbiome). The key is thought to be their high fibre intake which can reach up to 120 grams a day. A modern diet low in fibre is the top reason for microbiome depletion. Fibre supplements don’t improve the microbiome – only whole foods do.


Some consider the microbiome to be a separate organ and it runs on MAC -microbiota-accessible carbohydrates or as they are more commonly known – prebiotics. Prebiotics are the fibre and resistance starch that fuel our gut flora. Whole plant foods like fruit increase the gut flora. Not eating well can starve your microbial self – something seen in astronauts after returning from space where they had limited access to whole foods.


Flossing benefits the microbiome in your mouth and fibre benefits the microbiome in your gut. The effects of both are immediate. There are three things you need to restore your gut – prebiotics, polyphenols (health-promoting plant compounds) and probiotics.


What we eat can change the composition of our gut flora – for good or for ill -within twenty-four hours. The most important thing we can do to foster the growth of good gut bacteria is to keep them well fed with their favourite foods – fibre and resistance starch concentrated in wholegrains and legumes.


The best thing to have for jetlag

At one point he discusses pistachios which are the most melatonin rich nut with 0.2mg melatonin per gram. To get the physiological dose of melatonin all you need is TWO pistachios, which may be the best food to eat for jetlag – although he adds that the theory is unproven.


On smoothies vs soups

Studies showed that hot soup was more satiating than eating those same veggies in their solid state. Smoothies however were showed to be less satiating than fruit in their solid form. Both are liquid, which means chewing doesn’t affect it. The only real reason smoothies aren’t as filling, is because we gulp them down. Soup, which is hot is slowly sipped. If you sip your smoothie slowly it can be as filling as eating fruits and vegetable whole. Slowing down when eating satiates your hunger faster so you eat less and avoid overeating. Slow down by choosing foods that take more time to chew, take smaller bites and linger longer at the table to allow your satiety signals to take full effect.


On exercise

Food is more important than exercise when it comes to loosing weight. However, the biggest health benefit of exercise is that it helps get rid of our most dangerous body fat – the visceral fat around our internal abdominal organs. It burns the worst fat first.


On thylakoids

Thylakoids are the source of nearly all known life and the oxygen we breathe. It’s where photosynthesis takes place. When you eat greens like spinach, the thylakoid membranes can resist our digestive enzymes. They can last for hours in our intestines before getting broken down and it is in those hours, they work their magic. Thylakoid membranes bind lipase, the enzymes our bodies make to digest fat, thereby helping to block fat absorption. He compares them to fat blocker supplements, saying that if you want a fat blocker that is 100% natural without the side effects, eat spinach.


On habits

Healthwise it matters little what you eat on birthdays, holidays and special occasions. It’s the day to day that adds up, which is why eating habits are so important to health. Food choices may start out planned and purposeful but eventually morph into habit. Habits are hard to break no matter the intentions, which is why it’s often not enough to simply know what the right thing to do is. One way to change habits is using a method called implementation intentions: specific if-then plans to perform a specific behaviour in a specific context. If this happens, I will do that. If the triggers occur regularly, implementation intentions can turn into lifelong habits. To break a habit you need to select a new action. An alternative response is more effective than a non-response.


On fad diets

Most fad diets are rooted in legitimate science, but over time facts can get distorted, benefits overstated, and risks downplayed. Science ends up taking a backseat to marketing.


On how to prevent yourself from fainting

Many people experience fainting / near fainting spells when donating blood. According to Dr Greger, all you need to do to prevent yourself from getting woozy, is to simply chug two cups of water five minutes before getting stuck with the needle. The secret he explains is that a fainting spell can be dispelled due to a shift in the distribution of blood toward our centres, caused by the noradrenaline-induced peripheral artery constriction.




If you have an interest in nutrition, diets, weight loss or practice in those industries it’s a book you’ll likely find interesting and worthwhile. I know I did.

The studies are global, he even includes a line on Discovery’s Healthy Food cash back system to incentivise people to eat better, reducing illness and saving them money in the long-haul.

Much of his advice universal and doable like when he speaks at length about the health benefits of spices like turmeric, ginger and cinnamon. Those are easy and affordable ways to up your nutrition, and lots of us are already using these but perhaps more freely than in carefully measured portions added to every meal…


How Not to Diet was given to us by Pan Macmillan Publishers and is available here. Pan Macmillan Publishers nor the author approved or reviewed this piece prior to publication. Opinions + images are our own. 

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