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Does Diet Soda Really Cause Weight Gain?

In order to lose weight and cut fat you’ll need to consider all avenues. This means thinking about not only what you’re eating but drinking too.

Ultimately, you need to lower your calories. For some this means focusing on eliminating sugary snacks and choosing low-calorie substitutes. That way you can still have the occasion treat without going over on your daily energy needs.

In this article we’ll slice through the hearsay and tell you exactly what the research says about diet soda.

Will it really cause weight gain or can you consume it as part of a weight loss plan?

Read on to find out more…

What is Diet Soda?

Diet soda is a carbonated beverage. It’s much like your typical soda, the only difference is that it doesn’t contain sugar.

Back in the 1950s a new breed of drink was introduced which was claimed to revolutionize the drinks industry – a was a sugar free ginger ale drink made specifically for diabetics. It had no wider concerns over obesity, just a sweet drink that for the first time those with metabolic disease could enjoy.

It wasn’t until the 1960s that a wider range of diet drinks were released. Since then, manufacturers of these products have focused more on the weight loss market and become the biggest selling refreshments on the market.

They’ve been labelled as diet, sugar-free, no-cal or light  as well as a number of other weight loss-friendly terms.

And the marketing must be working as around 20% of Americans consume diet soda on a daily basis. It’s as popular now as it ever has been.

Artificial sweeteners

Instead of using sugar as a sweetener these refreshments are sweetened artificially with sucralose, aspartame, saccharin or acesulfame-k. These are synthetic compounds that are collectively referred to as non-nutritive sweeteners (NNUs).

The most popular of these – aspartame – is 200 times sweeter than table sugar. It provides the same amount of calories as sugar – 4kcal per gram – but because aspartame is used in such small amounts it’s calorie count is pretty much non-existent. Hence the ‘calorie-free’.

Many people suggest that sweeteners just don’t taste the same as sugar-sweetened beverages whereas others can’t tell the difference.

Diet Soda and Gut Enzymes

A study published in Applied Physiology, Nutrition and Metabolism [1], found that aspartame could interfere with a gut enzyme called intestinal alkaline phosphatase (IAP). This enzyme offers a protective role against obesity and diabetes, so when it is blocked, weight gain can occur.

But does diet soda cause weight gain or could it actually help you lose weight?

Let’s take a look at the research…

Does Diet Soda Help You Lose Weight?

Before we look specifically at diet soda it’s worth just taking a quick look at the quite damning research on sugar-sweetened sodas.

At 4kcal per gram, sugar can contribute massively to weight gain. Particularly when you consider that a typical can of soda contains as many as 8 teaspoons of sugar.

Sugary Soda and Weight Gain

There are a number of studies that show regular soda can increase weight gain.

For example, a the energy intake of group of female volunteers was found to increase by as much as 17% when asked to consume 450kcal of soda on top of their normal diet [2].

You’d have thought that the extra sugar calories might have evened themselves out elsewhere in the diet but the women didn’t compensate by eating less food.

Likewise, a study published in the prestigious JAMA [3] found that sugary soda consumption was highly correlated to weight gain. In their study of over 91,000 women, researchers found that 4-year weight gain peaked with the inclusion of one or more sodas per day.

Women that put less weight on were the ones that avoided sugar sodas altogether, or just had one occasionally.

A specific type of sugar called high-fructose corn syrup has also been found to contribute to weight gain. This corn starch-based sugar contributes to as many as 316 kcal per day in the modern US diet [4].

Although you’ll find this sugar in cakes, bakes and sweet, you’ll also find it in sugary drinks.

Key Point: Sugary soda has been found to increase overall daily energy intake and contribute to weight gain.

Is Diet Soda A Better Option?

With the damning research about sugary soda many people are turning to diet alternatives as a way of managing their weight. And that makes sense – no calories means no fat gain.

But an early study from 1990 released a pretty critical review of artificial sweeteners [5]. In the paper, a breakfast sweetened with aspartame was found to lead to higher overall energy consumption. Essentially, adding aspartame made the volunteers hungrier when compared to a sugary breakfast.

Of course this research looked specifically at breakfast not at soda so it’s hard to assess causality. All the same it’s bad for you if you want to lose weight.

Diet Soda and Weight Gain

There’s actually not a great deal of research showing correlation between diet soda, artificial sweeteners and weight gain. 

One study which is often cited by proponents of artificial sweeteners is this one from the San Antonio Heart Study [6]. In the study, 3,682 adults were tracked over an 8-year period. When data was analyzed, those who consumed diet soda were more likely to have a higher body mass.

The problem is though that this was only an observational study – this means that scientists had little control over volunteers and results are therefore less reliable. The results of this type of study are often subjective and led by bias.

Not All Studies Show Diet Soda is Bad

Recent research published in Obesity [7] used around 300 volunteers to look at how drinking either diet soda or water affected weight loss.

Each volunteers was spilt into one of two groups for a 1-year period:

  • 24 ounces of diet soda daily
  • 24 ounces of water daily

After 12 months the diet soda group has lost significantly more weight. The water group lost 2.45 kg on average but the soda group had lost a staggering 6.21 kg. 

They also felt less hungry, had lower cholesterol levels and felt that the soda had satisfied their cravings for sweet treats and foods.

Likewise, an 18-month trial of sugary and diet soda consumption in children also found diet drinks helped with weight loss [8]. Over a 18-month period, 641 children aged between 4 and 11 were given either 250 ml of either drink.

The sugar-free group lost significantly more weight as well as fat mass. 

Diet Soda and Exercise

An interesting study published in the American Journal of Clinical Nutrition [9] found that when combined with exercise, diet soda helped volunteers lose more weight than exercise alone.

Aspartame-sweetened beverages were associated with not only a significantly higher amount of weight loss, but also lower weight gain at a 2-year follow up.

Key Point: Research into diet soda and weight gain is inconclusive. Some studies show it can help you lose weight and others show it causes weight gain.

Soda vs Diet Soda – Which is Best for Weight Loss

There’s no room for sugary soda to hide. Pretty much every study released shows that it contributes to higher calorie intake and weight gain. It’s a bad choice when you’re wanting to cut weight or improve body composition.

Diet soda fairs better. Some studies show that it can form part of a healthy lifestyle and contribute towards weight gain. But be cautious though because some studies say the opposite.

In reality if you have the choice then avoid both. But if it’s one or the other then we’re saying diet is the way forward.

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  1. Hodin, RA et al. Inhibition of the gut enzyme intestinal alkaline phosphatase may explain how aspartame promotes glucose intolerance and obesity in mice. Applied Physiology, Nutrition, and Metabolism, 10.1139/apnm-2016-0346
  2. DiMeglio, DP et al. Liquid versus solid carbohydrate: effects on food intake and body weight. Int J Obes Relat Metab Disord. 2000; 24(6): 794-800
  3. Schulze, MB et al. Sugar-Sweetened Beverages, Weight Gain, and Incidence of Type 2 Diabetes in Young and Middle-Aged Women. JAMA. 2004; 292(8)
  4. Bray, GA et al. Consumption of high-fructose corn syrup in beverages may play a role in the epidemic of obesity. Am J Clin Nutr. 2004; 79(4): 537-543
  5. Mattes, R et al. Effects of aspartame and sucrose on hunger and energy intake in humans. Physiol Behav. 1990; 47(6): 1037-44
  6. Fowler, SP et al. Fueling the obesity epidemic? Artificially sweetened beverage use and long-term weight gain. Obesity (Silver Spring). 2008; 16(8): 1894-900
  7. Peters, JC et al. The effects of water and non‐nutritive sweetened beverages on weight loss and weight maintenance: A randomized clinical trial. Obesity. 2016; 24(2): 297-304
  8. de Ruyter, JC et al. A trial of sugar-free or sugar-sweetened beverages and body weight in children. N Engl J Med. 2012. 11; 367(15): 1397-406
  9. Blacburn, GL et al. The effect of aspartame as part of a multidisciplinary weight-control program on short- and long-term control of body weight. Am J Clin Nutr. 1997; 65(2): 409-18