Nowadays, more and more people prefer takeaway food. Takeout is popular because of its variety, convenience, and taste. However, its disadvantage is also obvious [1]. From the perspective of taste, different types of restaurants have different tastes, from spicy to salty. Excessive ingestion of spicy food and salty food, however, invites health problem. Salt is an indispensable condition in people’s daily diet. Almost all foods need to use salt to improve their taste. Chinese medicine believes that a salty taste enters the kidneys. It has the function of regulating the osmotic balance of human cells and blood and normal water and sodium. Potassium metabolic function, especially after a lot of sweating, properly supplemented with light saline can avoid the symptoms of electrolyte disturbance [2]. However, excessive salt intake is also a prominent problem in today’s diet, which also increases the occurrence of some chronic non-communicable diseases [3]. A high-salt diet is the first dietary risk factor for cardiovascular metabolic death in Chinese residents. A high-salt diet will aggravate the mechanism of cerebral ischemic injury. Excessive intake of salt in the daily diet will become an important risk factor in the development of cerebral ischemic disease [4]. One of the common causes of hypertension is excessive salt intake. Hypertensive patients who do not strictly control sodium intake in their daily diet may aggravate the symptoms and course of hypertension [5] [6]. Studies have shown that reducing salt intake in the diet can delay or prevent the occurrence of antihypertensive treatment, can promote blood pressure reduction in patients with hypertension after receiving drug treatment, and may be a simple way to reduce cardiovascular morbidity and mortality cost-saving intermediaries [7]. Studies have shown that the salt intake of residents in northern China has reached an average of 11.2 grams per day, which is a decrease from 12.8 grams in the 1980s. The salt intake of residents in the South increased from an average of 8.8 grams per day in the 1980s to 10.2 grams today [8]. According to the “Dietary Guidelines for Chinese Residents”, the daily salt intake of Chinese residents should not exceed 6 g [9]. This study selects Beijing, Shanghai, and Zhejiang, three large Chinese cities, which have a high frequency of Internet takeaway consumption. By analyzing the sodium content of takeaway food in these regions, the sodium content level in takeaway food was evaluated. Provide a basis for reducing the content of salt in takeaway food.

Collection and analysis of takeaway meals

For the purpose of this study, a takeaway meal was defined as food sold on an Internet platform, which was ready for immediate consumption. Regarding the Internet takeaway catering consumption data of local residents, select some takeaway restaurants in Beijing, Shanghai, and Hangzhou, and analyze the types of takeaway meals contained in the restaurants. This study collected a total of 4450 food items from 68 takeaway restaurants, including 30 in Beijing, 20 in Shanghai, and 18 in Hangzhou.

We collected various data of takeaway meals in randomly selected restaurants, including dish name, weight per serving, and weight of ingredients and accessories. According to the nature of takeaway meals and the types of main ingredients, takeaway meals were divided into two categories: Category 1: Chinese food, Western food, and Beverages; Category 2: Fried foods, spicy foods, meat dishes (meat, eggs, and aquatic products), vegetarian dishes (vegetables, soybeans and products), combined staple food, porridge, soup, and juices. According to the data in the “China Food Composition” (Volumes 1 and 2 of the Standard Edition), all ingredients in the takeaway food were calculated, and the sodium content in each serving and per 100 grams (edible portion) of the takeaway food was calculated respectively. The sodium content of raw materials and ingredients of takeaway meals that were not in the “China Food Composition” were replaced by the data of similar food.

Statistical analysis

The data were analysed using Excel tables and SPSS version 25, p < 0.05 was considered statistically significant, and results were shown as 95% confidence intervals. Due to non-normal distributions, data are expressed as medians with interquartile range (25^th and 75^th percentiles). The takeaway meals were classified into three groups according to their origin: 1) Chinese meals, 2) Western fast food, 3) Porridge. Salt levels in takeaway meals were compared with the China target of 6 g (Dietary guidelines for Chinese Residents, China, 2016).

In this study, takeaway meals from Beijing, Shanghai, and Hangzhou were selected as the research object. A series of data about takeaway meals were collected to analyze whether the sodium content in takeaways exceeded the standard. Now more and more people choose takeout to solve the three meals. According to the “Report on China’s Takeaway Industry Survey”, the overall development of the Chinese takeout industry is good in the first three quarters of 2019. It is expected that the annual takeaway transaction volume will exceed 600 billion yuan [10]. This also shows that takeaways are becoming an increasingly important part of daily life, and the safety of takeaways should be guaranteed. It is discovered in this study that the sodium content of takeaway food in the above mentioned three large cities exceeds the standard, which results in people who choose takeaway food taking in excessive sodium and which in turn causes a series of health problems [11].

In the results of this study, the sodium content of takeaway meals in Beijing