Do diet drinks make you fat?

This is a reoccurring question that we get from clients who have often heard conflicting views on the topic – can diet drinks cause weight gain or hinder efforts to get lighter? In particular, we get asked by those wanting to strip or really tone if diet drinks cause a rise in insulin levels. This is important because of the role insulin plays in both fat storage and metabolism.

Originally brought to the market for people with diabetes in the 1950s, diet drinks now make up around half of all sales of fizzy soda (or pop as we might call it in the UK). In 2018 diet coke actually overtook regular or “full fat” coke in global sales.Instead of sugar, artificial sweeteners are used to sweeten them., like aspartame, cyclamates, saccharin, acesulfame-k, or sucralose, Almost every popular sugar-sweetened beverage on the market has a “light” or a “diet” version — Diet Coke, Coke Zero, Pepsi Max, Sprite Zero, etc.

The role of insulin in fat gain

Insulin is a hormone or a chemical messenger. It is released into the blood when sugar levels become high – high sugar levels are damaging to us in both the short and long term. The insulin instructs the cells to take the blood sugar and store it in the adipose, or fat cells – although it is also stored in the muscles and liver as well. Simultaneously, as blood sugars are already high, we stop breaking down fat for fuel and releasing in into the blood. Thus we store fat while simultaneously ceasing to metabolise existing fat.

Diet drinks and insulin

Although some studies claim that diet drinks raise insulin levels, these are generally observational and not controlled experiments. Artificial sweeteners won’t raise your blood sugar levels in the short term. Some trials have shown mixed results, particularly depending on the type of sweetener used. A few studies have found sucralose to increase insulin levels by triggering receptors in our taste buds. However, few high-quality human trials exist, and it is currently unclear whether other artificial sweeteners have similar effects. Evidence for the main sweetener used in diet soda is clearer though – aspartame is perhaps the most well-known and studies  have shown no link to raised insulin levels. Further confirmation is that they are still deemed safe for diabetics.

Diet drinks and weight gain / loss

So with little effect on insulin do diet drinks help or hinder weight loss? Effects on weight loss are conflicting, but again the studies saying that they can increase weight remain observational, whereas controlled experimental studies show that replacing sugar-sweetened drinks with diet soda can result in weight loss.

One study had overweight participants drink 24 ounces (710 ml) of diet soda or water per day for 1 year. At the end of the study, the diet soda group achieved an average weight loss of 13.7 pounds (6.21 kg), compared with 5.5 pounds (2.5 kg) in the water group.

Our personal experience in 20 years of personal training – with most clients coming to us looking for at least an element of weight loss – shows that substituting full-fat soda for the diet version certainly helps clients create the calorific deficit needed for weight loss. However, it’s useful to note that when it comes to foods, the low-fat varieties are not always the best choice for weight loss, as they are not usually as filling or nutritious and have more additives and sugar in them.

So are diet drinks healthy?

In a word, no. Diet drinks like diet coke or sprite zero contain no useful nutrients. No fibre, no vitamins, no minerals. They are also detrimental to bone health, as we need to produce calcium carbonate to neutralise the acid in our stomach after drinking them. This diversion of calcium can cause osteoporosis. Their acidity is also bad for our teeth and in particular the enamel.

More seriously, observational studies have found an association between drinking large amounts of diet drinks and the development of kidney disease. The potential reason could be increased acid load on the kidneys due to its high phosphorus content.

Changes to the gut microbiome have also been found by studies; this is essential for many functions but in particular how we digest food and process carbohydrate, the implication here is that these changes might slow or hinder proper digestion

It is also worth pointing out that we have found diet drinks to be pretty addictive and hard to give up, both from our clients and our own personal experience!!

Find a better substitute

So although a big improvement over their sugar-loaded counterparts, diet drinks should only be consumed in moderation, and if possible find yourself a better alternative. Flavoured water, coffee, tea, diluted fruit juice and of course pure water are all better options.