Does Sugar Ruin Weight Loss? Here is what the Science Says

In this article, we will explore:

• What sugar is and the different types of sugar.
• Does sugar prevent weight loss?
• How does sugar affect appetite?
• Sugar and calories—how it impacts weight gain.
• Does the Glycaemic Index affect weight loss?
• Should you limit sugar intake while losing weight?

Types of Sugar

First, I will explain a bit about the types of sugar so that you have clear terminology when looking for information.

The most common sugars we encounter daily are:

• Regular table sugar (50% fructose and 50% glucose);
• High-fructose corn syrup (HFCS), increasingly used in sweetened drinks, including “carton juices”, nectars, etc. (42% fructose, 53% glucose, and 5% other sugars);
• Honey (38% fructose, 31% glucose, 7% maltose, 24% other sugars). Honey, of course, contains other beneficial substances, but this time we are focusing on sugar;
• Maple syrup (95% sucrose or table sugar, 4% glucose, and 1% fructose);
• Agave syrup (47% fructose, 16% glucose, and 37% other sugars). The final product usually only distantly resembles the original agave plant;
• Sugar alcohols such as xylitol, glycerol, sorbitol, maltitol, mannitol, and erythritol. These are neither sugar nor alcohol but are becoming popular as sweeteners. They do not cause rapid glucose spikes, but in excessive amounts, they can cause bloating and, in some cases, diarrhoea.  

Essentially, we distinguish between simple sugars or monosaccharides (e.g., glucose and fructose). If a “simple sugar” is combined with another sugar, it becomes a disaccharide. If the compound consists of three or more types of sugar, they are called polysaccharides.

The more complex the sugar, the more complex its breakdown, but ultimately, all sugars—even the most complex ones—become simple sugars that provide us with energy.

In nature, diverse sugar combinations occur. Fruit contains the simple sugar fructose. Milk contains a more complex sugar, lactose. What we are used to calling “sugar” in grocery stores is sucrose (glucose + fructose).

Does sugar itself cause weight gain?

It is often claimed that sugar is the primary cause of weight gain. However, research shows that weight changes are mainly determined by the total amount of calories consumed, not one specific type of nutrient.

If you consume more calories than your body burns, the excess energy is stored as fat regardless of whether it comes from sugar (carbohydrates), fats, or proteins.

Conversely, if you are in a calorie deficit (consuming fewer kcal than your body expends), weight loss can occur even if sugar is consumed in the diet.

Some studies have found that diets higher in added sugar are more frequently associated with weight gain.

However.

This effect arises not because sugar is being consumed, but because more calories are being taken in. In studies where total calorie intake is controlled, no significant differences in weight changes are observed between different carbohydrate sources.

This means sugar itself is not the cause of weight gain — the total energy value is what matters.

Another issue is that we often — frequently without even realising it — consume too much sugar or “liquid calories” through sweetened drinks, fruit juices, and similar products.

Does sugar affect appetite?

There is a belief that sugar significantly increases appetite or causes so-called “sugar spikes” (rapid rises in blood glucose), after which a person feels hungry.

However, scientific research shows that this effect is not so straightforward.

Many studies indicate that products with high added sugar provide less satiety than products high in fibre or protein.

This means that sweets may trigger a desire to eat more frequently for some people.

However.

This does not mean that sugar always causes overeating. Appetite is influenced by many factors — how much is eaten, the amount of fibre, protein, and fat in the meal, as well as your eating habits.

Research on the Glycaemic Index’s (GI) impact on appetite is also contradictory.

In some cases, rapid glucose fluctuations are linked to a faster onset of hunger, but the overall dietary structure is far more important here than one specific product or nutrient.

Does the sugar in fruit hinder weight loss?

Fruit contains natural sugars—mainly fructose, glucose, and sucrose.

Therefore, it is sometimes believed that fruit consumption should be significantly restricted during weight loss.

However.

Most research does not support this approach because, unlike sugary processed products, fruit also contains fibre, water, vitamins, and other biologically active compounds. Due to these properties, fruit is usually relatively low in energy/calories and promotes longer-lasting satiety.

Observational studies frequently find that people who regularly eat more fruit (and especially vegetables) have, on average, lower body weight and a lower risk of obesity. Intervention studies also show that including fruit in the diet usually does not interfere with weight reduction.

Of course, fruit also contains calories, so it should not be eaten in excessive quantities, but an apple or a banana as a snack can help you avoid overeating at lunch or dinner.

In short, in reasonable portions, fruit can be a wholesome and healthy part of the diet even during weight loss.

Should you give up sugar while slimming?

Both yes and no! 😊

The problem with sugar is that products containing it can lead to unplanned calorie intake, meaning you exceed your daily calorie requirement.

This, in turn, means the surplus will likely be converted into fat — you bite off a piece of chocolate and realise you can’t stop until it’s all gone — sounds familiar, doesn’t it? In this way, various snacks throughout the day can add up to many extra calories and, as a result, you feel like you’ve “hardly eaten anything,” but the weight keeps going up.

Sugar itself is not harmful, but we must monitor what and how much we eat. Often, we don’t even realise how much sugar (and thus calories) we are consuming. A good example is lemonade and especially “carton juices” — after all, juices are “healthy” and should be drunk, but read the nutrition facts label on the packaging…

Don’t misunderstand me; I am not against juices, only against the uncontrolled consumption of liquid calories. 😊

Stereotypes about the danger of sugar for weight loss

Most people simply want to lose weight — they don’t have the time to delve into physiological processes or scientific treatises on the effects of various food products on our bodies.

And so, stereotypes begin to flourish, spread primarily by friends and acquaintances who, in turn, have read or heard about it somewhere…

The stereotype—”if you want to lose weight, don’t eat sweets” — is so firmly embedded in the brain that it is perceived as an axiom. This stereotype is typically based either on outdated theories or simple personal fantasies. However, it is worth at least a superficial look at objective information sources, as it turns out everything is simpler than ever.

Research on sugar’s impact on weight loss

Based on the results of systematic research — both randomised and controlled — covering around 70 publications on the effect of sugar on body weight changes in children and adults, we can conclude that for people who do not strictly control their food intake, the main reason for weight gain is sugar intake (both directly and via sweet drinks). An increase in sugar in the diet leads to an increase in body mass; a decrease leads to weight loss.

The study results clearly show that sugar’s effect on body weight is directly related to the number of calories consumed — if you take in more calories than the body needs, weight increases; if fewer, it decreases.

Weight changes have nothing to do with the biochemical or physiological properties of simple sugar metabolism in our bodies. This conclusion is supported by multiple studies, which found that replacing simple sugars with other carbohydrates (especially those with a lower Glycaemic Index), while maintaining the same calorie count, does not cause body weight changes.

Glycaemic Index and sugar

Excluding sugar during weight loss is often justified by its high Glycaemic Index (GI). It is believed that “fast carbohydrates” are converted into fat rather than being used for the body’s energy needs.

There is not only no scientific evidence for such a view, but it also lacks simple logic — if cells did not use sugars under calorie (energy) deficit conditions, the body would receive even less energy, which would mean the energy shortage would have to be compensated even more from internal reserves (including fat), and weight loss should happen even faster.

In fact, scientists have already ended the dispute regarding the GI of carbohydrates in weight reduction. The study “Relevance of the Glycemic Index and Glycemic Load for Body Weight, Diabetes, and Cardiovascular Disease” (including 73 randomised controlled trials) concludes: “In existing intervention studies, there is insufficient evidence to support the benefits of low-GI carbohydrate sources in calorie-restricted diets aimed at weight loss.” And: “Controlled dietary studies suggest that changes in the GI of dietary carbohydrates do not affect the resulting body weight changes.”

The impact of fast and slow carbohydrates on lipogenesis

It is unclear where the belief originated that “fast carbohydrates” convert more into fat than “slow” ones, as scientific studies do not indicate this.

A special scientific conference, “The Relationship of Glycemic Index to Human Lipogenesis”, was even dedicated to this topic, which revealed no significant differences in the scale of fat synthesis from carbohydrates as a result of using polysaccharides (especially starch). It was found that for mono- and disaccharides, despite differences in blood insulin and glucose levels, no correlation is found between the GI of carbohydrates absorbed during the diet and their ability to activate lipogenesis (fat formation).

Should you limit sugar while losing weight?

Does the above mean that during a weight-loss diet, you shouldn’t worry about sugar intake?

No. We must not forget that a diet is not just a specific amount of calories and nutrients (protein, fat, carbohydrates), but also a dietary organisation tactic aimed at more or less comfortably maintaining an energy deficit.

Hunger becomes an insurmountable obstacle to weight loss for many. Therefore, you must be able not only to balance nutrients within a specific calorie deficit but to do it so that you feel full, and reducing sugar can be part of this tactic.

For example, sweetened drinks do not provide satiety, which often leads to their consumption in large quantities. Solid foods containing sugar are also very often characterised by high energy density (e.g., biscuits, ice cream, chocolate), which means it is much easier for people consuming such food to take in excessive calories compared to satiating low-calorie meals.

Furthermore, under conditions of restricted food consumption, the body’s levels of vital substances decrease: vitamins, minerals, trace elements, fibre, etc.

Sugar gives us “quick energy”, but the more we consume it, the more we are forced to exclude other carbohydrate sources, including those with high nutritional value, such as wholegrain products, legumes, fruit…

It’s simple — sugar consumption as such does not prevent weight loss. However, if there is too much of it, it will turn into fat (via the caloric surplus).

Observe moderation and read the ingredients on the packaging.  

Eat deliciously, eat balanced, keep moving, and —be healthy!