Our dietitian explains the ideas behind The Obesity Code by Dr. Jason Fung.
Each product we feature has been independently selected and reviewed by our editorial team. If you make a purchase using the links included, we may earn commission.
Credit: Photo: Getty Images

When it’s comes to cracking the root of American’s obesity crisis, there hasn’t been a solution that I’d put much money on—until I read The Obesity Code.

I didn’t think much about doing a diet review on The Obesity Code, a book that has been around since 2016, but has recently trended alongside popular eating approaches like Keto and intermittent fasting. I honestly dismissed it as another trendy weight loss approach.

I’m pretty leery of new diet books and products—or really any weight loss “solution.” Not only is there a lot of unhealthy, unsubstantiated advice out there, but it’s become more apparent over the past decade that we don’t have all the information to give consumers a true solution or to fully explain the U.S. obesity epidemic and how to fix it.

But my experience with The Obesity Code couldn’t have been more different. After highlighting my way through the book in under two days (something I haven’t done since grad school), I said, “THIS is the missing puzzle piece.” So what exactly is The Obesity Code? And how does it set itself apart from other diets like Keto and Paleo? I did some digging into this groundbreaking book—here’s what I found out.

What Is the Obesity Code?

Written by Dr. Jason Fung, The Obesity Code suggests that excess calories aren’t the underlying cause of obesity. Sure, cutting calories may cause short-term weight-loss, but these diets are never a long-term solution because the real, underlying issue hasn’t been addressed. Dr. Fung suggests that the real issue is a hormonal imbalance in the body due to years of poor eating and consistently elevated insulin levels—one that can’t be fixed by cutting calories, fat grams, or exercising more. The solution he proposes is that for long-term, sustained weight loss, key hormones like insulin must be reset and balanced within the body.

The Body’s Hormonal Imbalance

To better understand what Dr. Fung is proposing, here’s a super-simple overview of how insulin works. We eat food, which causes our insulin levels to rise and allows our body’s cells to use the food’s energy. Energy that’s not needed is stored as glycogen (short-term energy reserves in muscles and liver), and then as fat. Several hours later, as glucose levels drop, glycogen reserves are used for energy. Once glycogen is used up, the body starts breaking down fat stores for energy until we eat food and start the process over.

The Obesity Code suggests hormonal imbalances stem largely from today’s environment and food choices such as frequent snacking, eating because it’s mealtime and not because of hunger, and consuming an abundance of processed foods, refined carbs, and added sugars. The effect of each is that the body’s insulin levels stay elevated on a pretty consistent basis, which prevents the body from using fat as fuel and instead promotes fat storage. And this situation is exacerbated by stress, lack of activity, increasing body weight and insulin resistance.

The Obesity Code’s answer for correcting this is an approach that Dr. Fung started using with patients in his medical practice several years ago. Since then, his practice has grown to become a standalone clinic called Intensive Dietary Management (IDM) in Toronto. IDM is overseen by Program Director Megan Ramos. She and Dr. Fung have also recently started offering an online program with counseling.

How to Regain Hormonal Balance for Weight Loss

The Obesity Code highlights IDM’s approach to regaining hormonal balance, so a person can lose weight and successfully maintain that loss. It’s based on two key changes or recommendations. The first is incorporating short periods of intermittent fasting on a regular basis. The second is to choose whole, unprocessed foods that trigger only a small or minimal insulin response. This means eating foods such as:

  • Vegetables that grow above the ground
  • Legumes, soy, lentils, seeds and nuts
  • Some fruits, such as apples and berries
  • Animal protein sources, including full-fat dairy
  • Unprocessed fats, such as olive oil and butter

These foods end up providing a low- or lower-carb diet that’s high in natural fats and moderate in protein. Other fruits, processed whole grains, and root vegetables can be consumed, but less often, since they elicit a greater insulin response, and refined grains and added sugars should be minimized as much as possible.

Downsides of The Obesity Code

Unlike most popular diets books out there, The Obesity Code doesn’t set specific macronutrient ranges or a max limit for net carbs. Similarly, a few sample menus are provided and fasting times are suggested, but there’s fluidity to allow for individual adaptation based on needs.

The last quarter of the book gives you guidelines on what foods to eat, when to eat, as well as other lifestyle recommendations, but you won’t find a 6-week menu plan and exact parameters for intake or fasting like you would normally see at the end of other diet books.  

As a dietitian, I think this creates a healthy, sustainable approach, but some consumers may be frustrated by this lack of specificity or dictated eating prescription.

How Is The Obesity Code Different from Other Diets?

Not only is it research-based, but Dr. Fung’s explanation is one that can thoroughly answer why calories aren’t equal and why the obesity crisis hasn’t been solved. He takes small components and key ideas from popular eating approaches—such as keto, paleo, and Whole30—that have some promising effects on different aspects of obesity, weight loss, and food intake, but are not a solution and are a bit restrictive.

The result is an adaptable, sustainable plan where no foods are off limits and no food groups are excluded while addressing larger underlying issues related to hormones, appetite, insulin resistance and fat storage. It’s an explanation that makes all the other puzzle pieces in obesity research, weight loss, and nutrition science come together and fit for me as a dietitian.