Do Sodas Cause Obesity?

Do Diet Sodas Make You Fat?

Written by Dr. Steve Chaney on . Posted in Food and Health, Issues

Should You Kick the Diet Soda Habit?

Author: Dr. Stephen Chaney

Do Sodas Cause Obesity?We are consuming ever increasing amounts of diet sodas to combat the obesity epidemic. In 1960 14% of the U.S. population was obese and 3.3% of us consumed diet sodas. By 2010 41% of the U.S. population was obese and 20% of us were consuming diet sodas. It’s pretty clear that diet sodas aren’t helping us solve the obesity epidemic, but are they actually part of the problem?

You’ve probably seen the headlines questioning whether diet sodas actually help you lose weight. In fact many of the headlines imply the diet sodas will cause you to gain weight. Two of the more sensational headlines I came across said “Think diet sodas help you lose weight? Not so, Purdue study finds”, and “Can diet sodas actually cause more weight gain than regular sodas?”

Let me start with the first headline. The Purdue publication referred to in the headline (Swithers, Trends in Endocrin. & Metab., 24: 431-441) wasn’t really a study, it was an opinion piece. That simply means that it was a review where the references were selected on the basis of the author’s opinion. That’s OK if you clearly label it as an opinion piece, which Dr. Swithers did.

Now for the second headline: There is no good evidence that diet sodas will cause you to gain more weight than regular sodas. However, a number of published studies suggest that consumption of diet sodas is associated with weight gain – sometimes just as much weight gain as consumption of the sugar sweetened sodas they replace.

Do Diet Sodas Make You Fat?

The evidence that Dr. Swithers (Trends in Endocrin. & Metab., 24: 431-441) cited was pretty impressive.

For example, the San Antonio Heart Study recorded consumption of diet sodas and regular sugar sweetened sodas in 3,862 adults (average age 44) and measured the increase in BMI (a measure of obesity) over the next 7-8 years. That study found:

  • Individuals consuming >21 diet sodas/week were almost 2-fold more likely to become overweight or obese than individuals consuming no sodas.
  • There was a clear dose response effect, with a 41% increased risk of becoming overweight or obese for each can or bottle of diet soda consumed/day.
  • The increase in weight associated with diet soda consumption was just as great for those who were at normal weight at the beginning of the study as it was for those who were obese at the beginning of the study.
  • In this study the increase in weight associated with soda consumption was greater for diet sodas than it was for regular sodas.

Another major study (Circulation, 116: 480-488, 2007) recorded diet and regular soda consumption in 6039 participants in the Framingham Heart Study (average age 53) and measured the increase in obesity (along with other parameters associated with metabolic syndrome or pre-diabetes) over the next 4 years. This study found:

  • Individuals consuming one or more sodas/day had a 48% increased risk of becoming obese compared to people with infrequent soda consumption.
  • In this study the weight increase associated with soda consumption was virtually the same for diet sodas and regular sodas.

Are These Studies True?

Diet SodaThese, and similar studies have been criticized because they are looking at associations, which do not prove cause-and-effect. For example, it’s not always clear whether the people in those studies gained weight because they were consuming diet sodas or consumed diet sodas because they were overweight.

That argument is less persuasive for the San Antonio Heart Study, because the weight gain associated with diet soda consumption was also seen with people who were at normal weight at the beginning of the study. Still there is a need for good double blind, placebo controlled intervention studies.

There have been very few intervention studies in which one group of subjects were told to drink only diet sodas and the other group only regular sodas. Unfortunately, in those studies the total caloric intake of the diet soda group was also restricted. So while the diet soda group did lose weight, it’s not clear whether that weight loss was due to the diet sodas or the overall caloric restriction of the diet.

You may have also seen the recent headlines from a study showing that people consuming diet sodas gained no more weight than people consuming water (Obesity, 22: 1415-1421, 2014). But once again, both groups were given detailed instructions on how to restrict total calories. Almost any diet will work if you have a dietitian looking over your shoulder and telling you how to restrict calories.

So what is the average consumer to think? On the one hand, dietitians and health professionals are telling you to drink diet sodas if you want to lose weight. On the other hand, you keep seeing these headlines saying the diet sodas may not help you lose weight or may even cause you to gain weight.

Of all the recent blogs and online articles on the topic, the only one I actually recommend reading is from WebMD (http://www.webmd.com/diet/features/diet-sodas-and-weight-gain-not-so-fast).

WebMD often adheres to the AMA line, but I found this to be a very balanced analysis of the science behind the question of whether diet sodas help or hinder weight loss.

How Could Diet Sodas Possibly Cause Weight Gain?

The million dollar question is: How could diet sodas possibly cause weight gain? After all, they contain no calories. I think the most useful perspective from the Web MD article is that it’s probably not the diet sodas themselves that cause weight gain. It’s what we eat with the diet sodas that cause the weight gain. Here are a couple of quotes I found particularly enlightening.

Dr. Barry Popkin, a colleague from the University of North Carolina, calls it the “Big Mac and Diet Coke” mentality. He says: “Especially in America, we have a lot of people who eat high-fat, high-sugar diets, but also drink diet sodas.”

Why is that? Dr. David Katz from Yale University has research suggesting that artificial sweeteners may condition people to want to eat more sweet foods. He says: “Our taste buds don’t really differentiate between sweet in sugar and sweet from, say, aspartame. The evidence that this sweet taste is addictive is pretty clear. What I have seen in my patients is that those who drink diet soda are more vulnerable to processed foods with added sugars.”

There is some independent evidence to back up that hypothesis. For example, one recent study showed that rats given artificially sweetened yoghurt with their rat chow ate more rat chow and gained more weight than rats fed sugar-sweetened yoghurt with their rat chow (Behavioral Neuroscience, 122: 161-173, 2008). Another study in humans showed that consumption of artificial sweeteners activates a portion of the brain associated with cravings for sweets (Physiology & Behavior, 107: 560-567, 2012).

However, this viewpoint is controversial. Some experts think that the association between diet sodas and weight gain is psychological rather than physiological. Simply put, when people consume diet drinks they feel that they can splurge elsewhere.

The Bottom Line

  • Once again there is no magic bullet. There is no good evidence that diet sodas will help you lose weight unless you carefully control the calories in everything else you eat. And, diet sodas may just cause you to gain weight because they make you crave the very foods that are worst for your waistline.
  • In addition, there may be other good reasons not to consume diet sodas. For example, recent studies have shown that consumption of diet sodas may be linked to increased risk of metabolic syndrome or pre-diabetes (Circulation, 116: 480-488, 2007) and heart disease (see Does Sugar Cause Heart Disease? and Can Soft Drinks Cause Heart Disease?
  • My recommendations are to drink water, herbal teas, unsweetened tea & coffee or unsweetened mineral water or seltzer – perhaps with a splash of fruit juice.
  • Finally, there is no substitute for a healthy, calorie controlled diet; exercise; and lifestyle change if you want to lose weight and keep it off.

These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure or prevent any disease.

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Comments (1)

  • Mike Lucas

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    Great info Dr. Chaney! Thank you for the insight! Much appreciated!

    Mike & Jenn
    Shaklee Distributors
    Superior, WI

    Reply

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Latest Article

A Low Carb Diet and Weight Loss

Posted January 15, 2019 by Dr. Steve Chaney

Do Low-Carb Diets Help Maintain Weight Loss?

Author: Dr. Stephen Chaney

 

low carb dietTraditional diets have been based on counting calories, but are all calories equal? Low-carb enthusiasts have long claimed that diets high in sugar and refined carbs cause obesity. Their hypothesis is based on the fact that high blood sugar levels cause a spike in insulin levels, and insulin promotes fat storage.

The problem is that there has been scant evidence to support that hypothesis. In fact, a recent meta-analysis of 32 published clinical studies (KD Hall and J Guo, Gastroenterology, 152: 1718-1727, 2017 ) concluded that low-fat diets resulted in a higher metabolic rate and greater fat loss than isocaloric low-carbohydrate diets.

However, low-carb enthusiasts persisted. They argued that the studies included in the meta-analysis were too short to adequately measure the metabolic effects of a low-carb diet. Recently, a study has been published in the British Medical Journal (CB Ebbeling et al, BMJ 2018, 363:k4583 ) that appears to vindicate their position.

Are low carb diets best for long term weight loss?

Low-carb enthusiasts claim the study conclusively shows that low-carb diets are best for losing weight and for keeping it off once you have lost it. They are saying that it is time to shift away from counting calories and from promoting low-fat diets and focus on low-carb diets instead if we wish to solve the obesity epidemic. In this article I will focus on three issues:

  • How good was the study?
  • What were its limitations?
  • Are the claims justified?

 

How Was The Study Designed?

low carb diet studyThe investigators started with 234 overweight adults (30% male, 78% white, average age 40, BMI 32) recruited from the campus of Framingham State University in Massachusetts. All participants were put on a diet that restricted calories to 60% of estimated needs for 10 weeks. The diet consisted of 45% of calories from carbohydrate, 30% from fat, and 25% from protein. [So much for the claim that the study showed low-carb diets were more effective for weight loss. The diet used for the weight loss portion of the diet was not low-carb.]

During the initial phase of the study 161 of the participants achieved 10% weight loss. These participants were randomly divided into 3 groups for the weight maintenance phase of the study.

  • The diet composition of the high-carb group was 60% carbohydrate, 20% fat, and 20% protein.
  • The diet composition of the moderate-carb group was 40% carbohydrate, 40% fat, and 20% protein.
  • The diet composition of the low-carb group was 20% carbohydrate, 60% fat, and 20% protein.

Other important characteristics of the study were:

  • The weight maintenance portion of the study lasted 5 months – much longer than any previous study.
  • All meals were designed by dietitians and prepared by a commercial food service. The meals were either served in a cafeteria or packaged to be taken home by the participants.
  • The caloric content of the meals was individually adjusted on a weekly basis so that weight was kept within a ± 4-pound range during the 5-month maintenance phase.
  • Sugar, saturated fat, and sodium were limited and kept relatively constant among the 3 diets.

120 participants made it through the 5-month maintenance phase.

 

Do Low-Carb Diets Help Maintain Weight Loss?

low carb diet maintain weight lossThe results were striking:

  • The low-carb group burned an additional 278 calories/day compared to the high-carb group and 131 calories/day more than the moderate-carbohydrate group.
  • These differences were even higher for those individuals with higher insulin secretion at the beginning of the maintenance phase of the study.
  • These differences lead the authors to hypothesize that low-carb diets might be more effective for weight maintenance than other diets.

 

What Are The Pros And Cons Of This Study?

low carb diet pros and consThis was a very well-done study. In fact, it is the most ambitious and well-controlled study of its kind. However, like any other clinical study, it has its limitations. It also needs to be repeated.

The pros of the study are obvious. It was a long study and the dietary intake of the participants was tightly controlled.

As for cons, here are the three limitations of the study listed by the authors:

#1: Potential Measurement Error: This section of the paper was a highly technical consideration of the method used to measure energy expenditure. Suffice it to say that the method they used to measure calories burned per day may overestimate calories burned in the low-carb group. That, of course, would invalidate the major findings of the study. It is unlikely, but it is why the study needs to be repeated using a different measure of energy expenditure.

#2: Compliance: Although the participants were provided with all their meals, there was no way of being sure they ate them. There was also no way of knowing whether they may have eaten other foods in addition to the food they were provided. Again, this is unlikely, but cannot be eliminated from consideration.

#3: Generalizability: This is simply an acknowledgement that the greatest strength of this study is also its greatest weakness. The authors acknowledged that their study was conducted in such a tightly controlled manner it is difficult to translate their findings to the real world. For example:

  • Sugar and saturated fat were restricted and were at very similar levels in all 3 diets. In the real world, people consuming a high-carb diet are likely to consume more sugar than people in the other diet groups. Similarly, people consuming the low-carb diet are likely to consume more saturated fat than people in the other diet groups.
  • Weight was kept constant in the weight maintenance phase by constantly adjusting caloric intake. Unfortunately, this seldom happens in the real world. Most people gain weight once they go off their diet – and this is just as true with low-carb diets as with other diets.
  • The participants had access to dietitian-designed prepared meals 3 times a day for 5 months. This almost never happens in the real world. The authors said “…these results [their data] must be reconciled with the long-term weight loss trials relying on nutrition education and behavioral counseling that find only a small advantage for low carbohydrate compared with low fat diets according to several recent meta-analyses.” [I would add that in the real world, people do not even have access to nutritional education and behavioral modification.]

 

low carb diet and youWhat Does This Study Mean For You?

  • This study shows that under very tightly controlled conditions (dietitian-prepared meals, sugar and saturated fat limited to healthy levels, calories continually adjusted so that weight remains constant) a low-carb diet burns more calories per day than a moderate-carb or high-carb diet. These findings show that it is theoretically possible to increase your metabolic weight and successfully maintain a healthy weight on a low-carb diet. These are the headlines you probably saw. However, a careful reading of the study provides a much more nuanced viewpoint. For example, the fact that the study conditions were so tightly controlled makes it difficult to translate these findings to the real world.
  • In fact, the authors of the study acknowledged that multiple clinical studies show this almost never happens in the real world. These studies show that most people regain the weight they have lost on low-carb diets. More importantly, the rate of weight regain is virtually identical on low-carb and low-fat diets. Consequently, the authors of the current study concluded “…translation [of their results to the real world] requires exploration in future mechanistic oriented research.” Simply put, the authors are saying that more research is needed to provide a mechanistic explanation for this discrepancy before one can make recommendations that are relevant to weight loss and weight maintenance in the real world.
  • The authors also discussed the results of their study in light of a recent, well-designed 12-month study (CD Gardener et al, JAMA, 319: 667-669, 2018 ) that showed no difference in weight change between a healthy low-fat versus a healthy low-carbohydrate diet. That study also reported that the results were unaffected by insulin secretion at baseline. The authors of the current study noted that “…[in the previous study] participants were instructed to minimize or eliminate refined grains and added sugars and maximize intake of vegetables. Probably for this reason, the reported glycemic load [effect of the diet on blood sugar levels] of the low-fat diet was very low…and similar to [the low-carb diet].” In short, the authors of the current study were acknowledging that diets which focus on healthy, plant-based carbohydrates and eliminate sugar, refined grains, and processed foods may be as effective as low-carb diets for helping maintain a healthy weight.
  • This would also be consistent with previous studies showing that primarily plant-based, low-carb diets are more effective at maintaining a healthy weight and better health outcomes long-term than the typical American version of the low-fat diet, which is high in sugar and refined grains. In contrast, meat-based, low-carb diets are no more effective than the American version of the low-fat diet at preventing weight gain and poor health outcomes. I have covered these studies in detail in my book “Slaying The Food Myths.”

Consequently, the lead author of the most recent study has said: “The findings [of this study] do not impugn whole fruits, beans and other unprocessed carbohydrates. Rather, the study suggests that reducing foods with added sugar, flour, and other refined carbohydrates could help people maintain weight loss….” This is something we all can agree on, but strangely this is not reflected in the headlines you may have seen in the media.

The Bottom Line

 

  • A recent study compared the calories burned per day on a low-carb, moderate-carb, and high-carb diet. The study concluded that the low-carb diet burned significantly more calories per day than the other two diets and might be suitable for long-term weight control. If confirmed by subsequent studies, this would be the first real evidence that low-carb diets are superior for maintaining a healthy weight.
  • However, the study has some major limitations. For example, it used a methodology that may overestimate the benefits of a low-carb diet, and it was performed under tightly controlled conditions that can never be duplicated in the real world. As acknowledged by the authors, this study is also contradicted by multiple previous studies. Further studies will be required to confirm the results of this study and show how it can be applied in the real world.
  • In addition, the kind of carbohydrate in the diet is every bit as important as the amount of carbohydrate. The authors acknowledge that the differences seen in their study apply mainly to carbohydrates from sugar, refined grains, and processed foods. They advocate diets with low glycemic load (small effects on blood sugar and insulin levels) and acknowledge this can also be achieved by incorporating low-glycemic load, plant-based carbohydrates into your diet. This is something we all can agree on, but strangely this is not reflected in the headlines you may have seen in the media.
  • Finally, clinical studies report averages, but none of us are average. When you examine the data from the current study, it is evident that some participants burned more calories per hour on the high-carb diet than other participants did on the low carb diet. That reinforces the observation that some people lose weight more effectively on low-carb diets while others lose weight more effectively on low-fat diets. If you are someone who does better on a low-carb diet, the best available evidence suggests you will have better long-term health outcomes on a primarily plant-based, low-carb diet such as the low-carb version of the Mediterranean diet.

For more details read the article above.

 

 

These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure or prevent any disease.

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