Advancements in technology have significantly altered people’s lifestyles, leading to extended periods of sitting and reduced physical activity, which lower overall energy expenditure.(p1) Simultaneously, technology has transformed the food industry, often resulting in over-processed and substandard food products circulating in the market. These changes make it harder for individuals to identify healthy options, increasing the likelihood of consuming unhealthy foods and raising energy intake. This combination of decreased energy expenditure and increased energy consumption is mutually reinforcing, making obesity an unavoidable and critical issue that urgently needs to be addressed to improve human health. The development of some diseases is positively associated with obesity, including cardiovascular diseases, type 2 diabetes (T2D), non-alcoholic fatty liver disease (NAFLD), osteoarthritis, infertility, fatty kidney, and cancers.(p2) As of 2020, the global overweight population has reached 2.2 billion, with overweight or obese adults accounting for 42% of the total adult population.(p3) It is projected that by 2030, 50% of adult men and women worldwide will have a high body mass index (BMI). Notably, the prevalence of high BMI is higher in high-income countries, with a more pronounced trend among the elderly population, whereas in low-income countries, it is more common among younger groups.(p4) The development of obesity as a result of an imbalance between energy intake and expenditure is a commonly accepted view. However, the energy metabolism of the human body is very complex, and obesity occurs when the intake of energy exceeds the energy consumed by the body. There are many factors that can lead to obesity, not only limited to genetics, but also including overeating, peer pressure, social culture, low fitness level, chronic fatigue, and other factors.(p5)

Seaweeds are producers in marine ecosystems, providing energy for the growth and development of other marine organisms. Edible seaweeds also provide a rich and renewable supply of essential macronutrients and micronutrients, and serve as low-calorie foods consumed in large quantities in the Asian region, especially in China, Japan, and Korea.(p6) However, their nutritional value might vary depending on the geographical location, season, growth stage, and portion of seaweed harvested.(p7) Seaweed is extremely rich in carbohydrates, which generally make up about 50% of the dry weight and become oligosaccharides after digestion in the human body. Oligosaccharides are able to regulate the balance of flora in the intestinal tract. In addition, according to previous studies, phytochemicals such as fucoxanthin, polyphenols, and carotenoids have the potential to act as prebiotics.(p8)

Obesity is the trigger of many chronic diseases, and increasing attention is being paid to its control. However, it should be emphasized that few drugs are available today for the treatment of obesity, and the negative effects of these drugs have always been a major challenge to their clinical application.(p9) Hence, researchers tend to discover more safe and effective anti-obesity ingredients from natural products, especially phytonutrients. Seaweeds are important resources that are being developed because they are easy to cultivate, safe, and rich in ingredients.(p10) This review primarily focuses on the experimental models for obesity research and the anti-obesity efficacy of natural products derived from seaweeds.