Sweet truths and bitter pills: How free sugars affect human health

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In a recent review article published in Nutrients, researchers summarized the current evidence about the effect of free sugars on health outcomes in humans, including mood, cognition, cardiovascular disease, diabetes, and obesity.

They concluded that excessive consumption of added sugars may adversely affect health and overall well-being outcomes, highlighting the need for further research into how different carbohydrate forms affect diverse populations.

Study: The Impact of Free Sugar on Human Health—A Narrative Review. Image Credit: qoppi/Shutterstock.comStudy: The Impact of Free Sugar on Human Health—A Narrative Review. Image Credit: qoppi/Shutterstock.com


Noncommunicable diseases (NCDs), including chronic conditions like heart disease and diabetes, are largely preventable but account for a significant portion of global deaths.

While researchers have emphasized lifestyle modifications to prevent and treat NCDs, with evidence suggesting that an improved diet yields significant benefits, the specific role of sugar consumption has been debated.

In the late 20th century, reduced fat consumption led to increased intake of carbohydrates and added sugars, notably high-fructose corn syrup. This coincided with rising obesity, diabetes, and heart disease rates.

Recent years saw a slight decline in sugar intake, prompted by health guidelines advocating limited daily sugar intake to mitigate health risks.

Some studies have linked excess consumption of sugar to various health issues. At the same time, other research indicates that sugar might not be inherently more harmful than other energy sources in the diet.

Effects of sugar on health

Global obesity rates have risen significantly over the past decades, with obesity linked to various NCDs. The debate over the primary cause of obesity—excess sugar, fat, or total calorie intake—continues, with recent declines in sugar consumption alongside persistent obesity rates suggesting generational effects.

Studies comparing low-carbohydrate and low-fat diets revealed varied results, highlighting the need for personalized dietary interventions.

Sugar consumption, particularly from fructose and sugary beverages, is associated with an increased risk of type 2 diabetes (T2DM) in numerous studies. However, findings are inconsistent, with some shorter-term studies failing to establish clear relationships.

Longer-term studies suggest a significant impact of fructose intake on insulin resistance and diabetes risk, especially in women. The protective effects of dietary fiber and certain fats on diabetes risk are also noted, indicating the complexity of dietary factors influencing T2DM.

The role of refined carbohydrates and sugary beverages in heart disease is increasingly recognized, with studies indicating their association with dyslipidemia and increased cardiovascular risk.

While some studies show a direct link between sugar consumption and heart disease, others find conflicting results, possibly due to differences in study duration and methodology.

Research suggests that sugars may play a detrimental role in cardiovascular health, although the specific types of carbohydrates and fats consumed may have different effects.

Chronic excessive sugar intake is hypothesized to impair cognitive function, with studies in animals and humans demonstrating neurological and cognitive impairments associated with high sugar consumption.

Maternal sugar consumption during pregnancy and breastfeeding may also impact offspring cognition.

While some studies suggest short-term cognitive benefits of sugar consumption, long-term effects are less clear and may be influenced by factors such as glucose control and dietary habits over time.

The impact of sugar on mood and behavior is debated, with inconsistent findings across studies. While short-term studies suggest potential mood benefits of sugar consumption, particularly following fasting, longer-term studies indicate correlations between high-sugar diets and depression, anxiety, and other mood disorders.

Confounders and methodological challenges complicate research on the relationship between added sugars and psychological health, warranting further investigation.

Underlying mechanisms

Chronic high sugar consumption is hypothesized to impact mood through neurological mechanisms. Western diets, high in sugar, are associated with inflammation, reduced BDNF in the hippocampus, and changes in dopamine signaling, resembling addictive behaviors.

Sugar consumption can dysregulate dopaminergic pathways, leading to increased sugar seeking and consumption, akin to addiction. Microbiome disruption, particularly by high sugar diets, exacerbates inflammation, contributing to obesity and neurodegeneration.

Sugar-induced dysbiosis may lead to gut permeability, triggering systemic inflammation and neuroinflammation, potentially explaining neurological and psychiatric impairments associated with sugar and obesity.


Minimal scientific evidence supports the claim that added dietary sugars confer health benefits; rather, a growing body of research indicates that they have negative effects, especially when consumption is excessive, prolonged, and high in fructose.

Glucose supplementation may be beneficial under certain circumstances but can also obtained from dietary sources, including whole grains, vegetables, and foods.

While not all added sugars need to be eliminated, nutritionists recommend limiting their intake to no more than 10% of total energy consumption.

The reviewers emphasized the need for further exploration of how different artificial sweeteners and macronutrients impact health outcomes and the challenges posed by sugar-related impairments.

While large-scale population studies may not be ideal for identifying individualized impacts, cohort studies and randomized controlled trials across diverse populations can yield insights into the precise effects of macronutrients and how they interact with each other to modify health outcomes.

Journal reference:
Priyanjana Pramanik

Written by

Priyanjana Pramanik

Priyanjana Pramanik is a writer based in Kolkata, India, with an academic background in Wildlife Biology and economics. She has experience in teaching, science writing, and mangrove ecology. Priyanjana holds Masters in Wildlife Biology and Conservation (National Centre of Biological Sciences, 2022) and Economics (Tufts University, 2018). In between master's degrees, she was a researcher in the field of public health policy, focusing on improving maternal and child health outcomes in South Asia. She is passionate about science communication and enabling biodiversity to thrive alongside people. The fieldwork for her second master's was in the mangrove forests of Eastern India, where she studied the complex relationships between humans, mangrove fauna, and seedling growth.


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