Is Sugar Fattening? It Depends

Is sugar the main obstacle preventing you from maintaining a healthy weight?

Recently, the World Health Organization (WHO) called for an international tax on sales of sugar-sweetened beverages. The thinking behind such a tax is that the growing epidemic of obesity in the world is caused by sugar-sweetened soda. However, this is contrary to the WHO Medical Officer that stated, “The decrease in soda sales in Mexico (who recently imposed a sugar tax on soda) is good news, but we don’t have conclusive evidence yet on whether this is actually reducing obesity and type 2 diabetes.”

Swapping Out Soda for Water May Not Impact Long-term Obesity

Harvard Medical School did a comprehensive study on reducing the use of sugar-sweetened soda in obese children by replacing them with free bottled water and intensive dietary consulting 1. The result after two years of extensive intervention was that there was no change in the levels of obesity in these children.

This is why nutrition is so complicated, and yet we try to make it too simple. Let’s start with obesity. Calories do count. If you consume more calories than you immediately need, you will store the excess (usually in your fat cells) for later use.

The Two Reasons We Overeat

There are two reasons why people overeat. One is apparent, and the other is less apparent.

  1. Tasty food – More palatable food activates the hedonic reward system, which makes you eat more food. The more palatable the food, the more dopamine the hedonic reward releases which overrides your calorie thermostat. This is why sugar is more palatable than non-starchy vegetables even when both supply the same levels of carbohydrates to the body.
  2. Inflammation in the energy-balance system in the hypothalamus – This is basically a “calorie thermostat” in the brain that balances the intake and burning of calories with great precision. This is explained more in my book, Toxic Fat 2 and also addressed within Our Brains Control Why We Eat – But You’re Much Smarter. One of the best ways to cause hypothalamic inflammation to generate an increase in calorie intake is to consume a high fat diet rich in palmitic acid (3-5).

Why We Can’t Solely Blame Sugar for Our Weight Issues

Added sugar makes soda, a snack, or any meal more palatable. This is why it is so prevalent in processed foods. The more palatable a food is, the more likely you are to eat it. In addition, added sugar also has a metabolic effect as it can stimulate insulin release to lower blood sugar and that will also make you hungry. Since it is very difficult to separate one mechanism from another, it’s easier just to make sugar the “evil one” and call it a day as the WHO has suggested. This same type of thinking was also used in Middle Ages to burn witches to order to get rid of the Black Plague.

Palatability May Be A Clue To Overconsumption

Genetic manipulation in mice has allowed the separation of the impact of sugar on the two mechanisms in the brain that control our intake of food 6. In this experiment, the sugar taste receptor was genetically knocked out in mice. When these mice were fed a high-sugar diet (by adding extra sugar to their water like a soda), they didn’t gain weight because it didn’t taste sweet. The metabolic effect of the sugar was still present, but the lack of palatability of the added sugar prevented any weight gain.

Then they added some fat to the sugar-sweetened water. Now the mice without the sweet taste receptors quickly become obese as the combination of the fat and the sugar in the water was affecting the hedonic reward system in the brain.

This is the secret that the food industry and dessert makers learned many years ago: the combination of sugar and fat is irresistible. This also helps explains why you have weight regain on high-fat, low-carbohydrate diets. First, they are rich in saturated fats (like palmitic acid) to distort the energy-balance thermostat in the hypothalamus so you eventually end up eating more calories than you need. Second, the fat activates the hedonic reward system so you eat more calories because the food is more palatable. End result is that you gain weight.

So let’s go back to the Harvard study on reducing the use of sugar-sweetened sodas. It was successful (the children drank less soda), but it didn’t reduce their obesity after two years. It doesn’t matter if you reduce the sugar unless you are also reducing the fat at the same time. This is why McDonald’s sells the combo package of the sugar-sweetened soda and fatty hamburger. Maybe this is why they call it a Happy (for our bottom line) Meal.

The Key To Avoid Weight Gain Is To Limit Both Sugar and Fat

The secret to treating obesity is to eat the least amount of calories without being hungry or tired. You do this by reducing diet-induced inflammation in the brain (by reducing omega-6 and saturated fats), and from bypassing the sweet receptors in the tongue (using low-glycemic carbohydrates such as non-starchy vegetables).

You still need the right balance of protein, carbohydrate, and fat to control the metabolic response of meal in the blood and the gut. Also, consider Zone PastaRx as your primary protein source. PastaRx is our patented protein-rich food product designed to stabilize blood sugar and curb hunger for hours.

If you can do everything I’ve recommended at each meal, you can restrict calories without hunger or fatigue for a lifetime. That is the promise of the Zone Diet.

Need additional support? Check out Zone Lifestyle Tips: 6 Ways to Tame Your Sweet Tooth to see how you can kick your sugar habit for good, despite how rewarding it may taste.


  1. Ebbeling CB et al. “A randomized trial of sugar-sweetened beverages and adolescent body weight.” N Engl J Med 367:1407-1416 (2012).
  2. Sears B. Toxic Fat. Thomas Nelson. Nashville, TN (2008).
  3. Kleinridders A et al. “MyD88 signaling in the CNS is required for development of fatty acid-induced leptin resistance and diet-induced obesity.” Cell Metab 10:249-259 (2009).
  4. Cintra DE et al. “Unsaturated fatty acids revert diet-induced hypothalamic inflammation in obesity.” PLoS One 7:30571 (2012).
  5. Sears B and Perry M. “The role of fatty acids in insulin resistance.” Lipids Health Disease 14:121 (2015).
  6. Glendinning et al. “The role of T1r3 and Trpm5 in carbohydrate-induced obesity in mice.” Physiol Behav 107: 50-58 (2012).

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About Dr. Barry Sears

Dr. Barry Sears is a leading authority on the impact of the diet on hormonal response, genetic expression, and inflammation. A former research scientist at the Boston University School of Medicine and the Massachusetts Institute of Technology, Dr. Sears has dedicated his research efforts over the past 45 years to the study of lipids. He has published 40 scientific articles and holds 14 U.S. patents in the areas of intravenous drug delivery systems and hormonal regulation for the treatment of cardiovascular disease. He has also written 14 books, including the New York Times #1 best-seller, The Zone, which have sold more than 6 million copies in the U.S. and have been translated into 22 different languages.


  1. chris stephens

    What do you think about the potential for resistant starches to play a roll in managing blood sugar? would you ever include them in any of your products?

  2. Dr. Arcadio P. Sincero

    Dr. Sears:

    If your AA is 7.9 and your EPA is 3.9, these values are within the target range for AA but just a little bit lower for EPA. However, if we compute the AA to EPA ratio, it is 7.9/3.9 = 2.0. This is a very ideal ratio for the AA/EPA ratio, in which the target is 1.5 to 3.0. With this ideal ratio of AA/EPA, would recommend increasing the dose for EPA? Thanks.

  3. Bryan Travis

    Palmitic acid is main component of our bodies as I understand fat storage, and would be the primary fatty acid released from fat cells during states of fasting (which per Taubes point of view is probably every night in a lower carb diet scenario) and of course during successful weight loss. I read Sears saying hypothalmic inflammation drives hunger but people who do paleo and intermittent fasting report that they do not suffer hunger, au contraire, despite pushing themselves into fasting states DAILY. So I’d….like to see the power of this inflammation effect fleshed out, but I remain curious/conflicted on it. Others say SatFatBad because it stimulates “Toll-like receptors, triggering (from memory) inflammation or some effect opposite of what eating a higher fat lower carb moderate protein intermittment fasting diet is meant to help you do.

    ALL OF THAT SAID, we consume a lot of Dr Sears brand Fish oil, and we take on board the polyphenols story fairly well too…though I suspect that the main effect must be within the gut and/or the gut walls, as a lot of those compounds don’t last long at all in our blood streams… Poor absorption through the gut walls and short half lives anywhere else seem to be the rule for most of those family and similar family compounds, though no all..

  4. Peter Parker

    Why is the work of Dr Robert Lustig from UC not cited? This is a glaring omission.

  5. Mark McGinn

    great article Barry, lots of paleo folks and followers of Dr Hyman and Dr Lugwig are loading up on the fat and keeping the carbs very low, do you think for some people this works fine but for others not ?


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