1. Introduction

The significant dietary diversity in Southeast Asian countries is largely attributed to the many ethnic and cultural food practices, as well as the degree of past and present foreign influence in the region^[1][2][3]. Being strategically situated along a major maritime East–West trade route, most countries in Southeast Asia were subject to some form of colonial governance for significant periods in the last few centuries. These factors have molded the cooking styles, taste profiles, as well as the ingredients available to each Southeast Asian country^[1]. Chinese immigrants brought along dishes such as noodles served in a broth, curried, or stir-fried with a variety of ingredients; many different types of dumplings and steamed buns; stir-fried, braised and steamed vegetable, fish and meat dishes that pair well with rice^[1]. Influence from the Indian subcontinent contributed to foods such as coconut-milk based curries, flatbreads and a myriad of spiced biryanis^[1]. European traders and colonial rule brought along with them bread and other bakery products, pate, salads, as well as many types of vegetables and herbs like cassava, tomatoes and papaya into the region^[1]. Many of these influences were adopted and integrated with local produce and flavors, resulting in significant variation throughout Southeast Asia. In more recent times, the wave of rapid globalization has also brought in a whole new set of flavors through the introduction of fast food into the region^[1][4][5][6].

All Southeast Asian countries are plural societies characterized by the presence of a dominant ethnic majority and an array of ethnic minorities^[1]. Therefore, ethnicity, culture and even religion has a pronounced impact on the choice of foods, types of local ingredients used, structure of meals and patterns of eating behavior. There are further distinctions between urban populations and rural villagers; between the wealthy and the poor; and between the educated and the less educated, and these factors greatly affect access, as well as choice of foods^[2][4]. This level of diversity can make it difficult for consumption patterns and behaviors to be accurately defined on a population level ^[1][4][7].

2. Complexity of the Southeast Asian Diet 

2.1. Meal Settings and Eating Practices

Meals in Southeast Asia are generally communal in nature and sharing of food from central platters is the typical practice^[1]. A common type of meal that demonstrates this practice is the consumption of rice paired with a variety of dishes such as curries, braised meats, steamed vegetables and soups^[1][8][2][5]. These dishes are often shared between guests at the table and individuals pick food from the central platters onto their own plates or bowls to be eaten with rice. Family meals for most Southeast Asian ethnicities consist of different dishes laid out on a table at the same time, to be picked from as preferred by the diners. At formal events and functions, these meals are also frequently served in a buffet line, allowing diners to pick their preferred choice of food from a variety of selections. At some functions, dishes are served sequentially one after another at the dinner table^[1].

The street food culture of Southeast Asia also facilitates the busy urban life. It serves an array of foods that can be easily purchased and consumed on the go, taken back home or brought to the workplace for consumption^[9][5][10]. This can range from full meals such as soup noodles or fried rice, to mid-meal snacks such as meat skewers, sandwiches, wraps and dumplings, as well as an assortment of bite-sized local kuih (traditional Southeast Asian pastries and cakes)^[1][10].

The purchase of food from these vendors is becoming more commonplace in recent years^[5][11]. Many Southeast Asian foods involve complex spice and herb pastes that are time-consuming to prepare and broths that can take hours to simmer^[1][5]. In the past, most of these meals were prepared at home but the increasing demands of the workforce have resulted in families having less time to make these authentic foods ^[10]. Increasingly, many urban families are choosing to either eat out at restaurants or food centers or to buy foods from street vendors to consume with rice at home^[1][10]. In 2010, 60.1% of the general adult population in Singapore were found to eat out at least four times a week, and a 1990 survey in Bangkok showed that families spent about half their monthly food expenditure on foods prepared outside the household^[1][5]. An increasing reliance on external food sources is a trend seen in many urban societies, and other rapidly urbanizing countries in Southeast Asia may also experience similar trends^[9].

From a nutrition standpoint, the vast variety of food sources can make it challenging for individuals to have an in-depth understanding into the types and proportions of ingredients used. Aside from the different recipes used by chefs and establishments, portion sizes can also vary significantly between sources. This dynamic food landscape can make it difficult to define, much less identify, a standardized portion size and can complicate the matching of a food to an item or items in a nutrition table.

2.2. Personalization of Meals

Many Southeast Asian foods involve a level of personalization. For example, noodle vendors in Malaysia or Singapore would ask customers for their preferred noodle type; if they prefer their noodles to be served dry or in a broth, and if they have a preference for chili or other sauces. Noodles from other Southeast Asian regions such as Vietnam and Thailand have similar features: Vietnamese rice noodles, also known as Pho, have platters of vegetables, herbs and condiments placed on the table for customers to help themselves and Thai boat noodles often have a tray of various dry and wet condiments placed at the table for diners to tailor their meals to their own personal tastes^[1].

Economy rice is a type of dish consumed by many of the major ethnicities in Southeast Asia, and there are a variety of terms used to describe the meal such as Mixed Vegetable Rice, Cai Fan, Nasi Campur, Nasi Padang or Banana Leaf Rice. The meal typically involves the selection of 2 to 4 dishes from an array of 10 to 30 dishes to be eaten with rice^[1]. Serving sizes for each of the dishes can be highly variable depending on the generosity of the stall attendant. Customers can also choose to have their rice doused with various types of curries or sauces, changing the overall profile of the meal to their liking^[1]. This degree of customization is also prevalent in the many communal meals that Southeast Asians partake in. Dishes are scooped from shared platters and placed into an individual’s own bowl or plate, to be eaten in the order and quantity of their choosing^[1][7].

Personalization and self-regulation is an integral part of Southeast Asian cuisine and can make assessment of population-wide consumption patterns problematic^[3]. This can confound generalized assumptions and mask specific nutritional issues that may be faced by certain population groups, making it difficult for population-wide nutrition policies to be implemented effectively.