The prosperity of a country, commonly measured in terms of its annual per capita Gross Domestic Product (GDP), has different relationships with population levels of body weight and happiness, as well as environmental impacts such as carbon emissions. The aim of this study was to examine these relationships and to try to find a level of GDP, which provides for sustainable economic activity, optimal happiness and healthy levels of mean body mass index (BMI). Spline regression analyses were conducted using national indices from 175 countries: GDP, adult BMI, mean happiness scores, and carbon footprint per capita for the year 2007. Results showed that GDP was positively related to BMI and happiness up to ∼$US3000 and ∼$5000 per capita respectively, with no significant relationships beyond these levels. GDP was also positively related to CO2 emissions with a recognised sustainable carbon footprint of less than 5 tonnes per capita occurring at a GDP of <$US15,000. These findings show that a GDP between $US5 and $15,000 is associated with greater population happiness and environmental stability. A mean BMI of 21–23 kg/m2, which minimises the prevalence of underweight and overweight in the population then helps to define an ideal position in relation to growth, which few countries appear to have obtained. Within a group of wealthy countries (GDP > $US30,000), those with lower income inequalities and more regulated (less liberal) market systems had lower mean BMIs.