How Junk Food Makes Your Brain Want to Get Fat (And How to Reverse it)

In the video above, endocrinologist Robert H. Lustig M.D. explains how the industrial global diet impairs the function of two hormones, insulin and leptin, which sets up a biochemical drive in our brains to eat more than we’re supposed to.

Leptin – The Body’s Energy Balance Hormone

Leptin is an incredibly important hormone in the body.

It is secreted by our fat cells. The bigger they get, the more leptin they secrete.

More fat = more leptin.

Leptin is supposed to send signals to the brain, informing it about how much body fat is stored.

We eat -> Body fat gets stored -> Leptin increases -> Brain “sees” the leptin and makes us stop eating.

Leptin Function Diagram

This is a basic negative feedback loop, the output (leptin) decreases the input (eating). This is how the brain is supposed to keep body fat levels within a narrow range over the long term.

The problem today is that leptin isn’t working.

Obese individuals have high levels of leptin, but it isn’t getting through to the brain and therefore there is no signal that the fat cells have enough energy stored and that the person needs to stop eating.

Insulin – Drives Fat Storage, Blocks Leptin

Diabetic Shooting Insulin

You’ve probably heard of insulin before.

It’s the hormone secreted by the pancreas after eating a meal with carbs in it (protein affects it too, to a lesser extent).

One of the other functions of insulin is that it makes the body synthesize fats out of glucose, then tells the fat cells to pick up as much fat as they can and store it.

This is one of the reasons diabetics start gaining weight when they start shooting insulin. Insulin drives fat into storage.

In addition to driving fat storage, insulin blocks the leptin signals in the brain (1, 2).

How to Reverse it

Bread Caution

If you’re already overweight/obese, then you are likely to have issues with these two hormones already.

Fortunately, the solution is incredibly simple. All you have to do is eat less sugars and starches (carbs).

This is the best way to lower insulin levels in the blood (3, 4, 5).

Eating less carbohydrates (especially from fructose) also lowers triglycerides, another known cause of leptin resistance (6, 7, 8).

If less carbs both lower insulin and improve leptin resistance, then they should be effective to reverse obesity, which they are (9, 10).

What About The Low-Fat, High-Carb Diet?

The failed low-fat diet may be good for lean people, but it is absolutely useless as a cure, probably because it does nothing to address the root causes of obesity, which include insulin and leptin resistance.

The largest randomized controlled trial ever conducted on diet, called the Women’s Health Initiative and included 48,835 postmenopausal women, revealed some interesting results:

The women on the low-fat diet were only 0,4kg (1 lb) lighter than the women eating the standard american diet after 7.5 years (11).

How’s that for a failure?

Of course, this massive study did not change the minds of the nutrition profession and they continue to peddle their failed diet.


  1. Hi Kris.. I’d like to ask you about some cheat days.. I know u don’t encourage to cheat but some days I just eat more than I should, I don’t eat junk foods on cheat days, I only eat slightly more than I should.. is this ok or should I cut off with it ?

  2. Hi. I am not overweight, but I would like to lose just five pounds to fit into all of my clothes. For four weeks, I stayed under 50 carbs a day… from strawberries, yogurt, and other healthy sources, but can’t seem to budge the last five. Any ideas? Thanks.

  3. Sandy Bryman says:

    What do you think of Atkins endulge bars they only contain 2 to 3 grams of carbs. I think they are great for a snack! They contain sugar alcohols so I dont know? You’re the expert. By the way I’ve lost 20 lbs and am maintaining it! Thanks.

  4. I enjoy a healthy clean diet. I keep a food diary to keep me on track. I exercise 5-6 times a week. I would like to drop about 20 more pounds, I have kept 40-45 pounds off for the past two years. I quit smoking one year ago (very proud) and basically maintained my weight the last year.

    My biggest problems are portion control (I love food) and intense cravings for chocolate. I’m like a choco-holic one bite and I just want more and more. I have read and tried everything to control these cravings and still have a hard time, any suggestions ?

    • When I have the chocolate craving, I use the 85% cocoa stuff. A small square is only like 2.5 grams of cars. The best way for me personally is to put a glob of peanut butter on it, then have a cup of hot coffee with it. It is also very good w/ a few fresh strawberries. Something about that bitter chocolate kind of makes one square great but two is overkill–at least in my experience. Hope it works for you!

    • I eat date balls to help with the choco-wants. I don’t remember where I got the info from and don’t follow a set recipe. I chop up about 20 dates, scissors are best as I find dates are hard to chop by machine. Mix with 1 tbls hot water and leave til the water is absorbed and the dates are soft. Mix in 2 tsp cocoa powder. Shape into balls and roll in coconut. This is quite messy if you do it in your hands – I pat heaped mixture into a teaspoon and scoop out with another spoon into the coconut. This makes about 7-8 balls. I do not know what the food value breakdown is but would be interested if someone can supply it

  5. I have tried every possible means to eat well but all in vain, I need your help.

  6. Yes, but remember this is just to stop the chocoholic binge!!

  7. Ifeoma Okere says:

    I am a mother of two and presently weigh 110 kg. I want to lose weight in order to be there for my Kids and hubby, but I can’t do anything right. Help.

  8. Mai Mustafa says:

    Hey Kris. How many apples can I eat per day? I once read that the apples are negative calorie food that my body needs more calories to burn than the calories an apple has. Is this true? I eat one when I feel hungry only :)

  9. Tanisha says:

    Thanks so much Kris!

    I have this debate I’m researching for at school about how fast food makes you fat and I was reading something about Leptin! This was easy to read and understandable! Other websites write them in a way that just confuses me! Again a big thank you! (I did not copy anything you wrote, I just needed a better understanding of what leptin was in order to write my speech)

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