Dieta vs. régimen
The Spanish words 'dieta', 'régimen', and 'régimen' all have the same translation in English as 'diet', especially in the context of slimming or weight loss. However, they are used differently based on contexts, and evoke different kinds of sentiments.
Dieta
This is the most general word for 'diet', referring to all food a person usually eats. It does not inherently suggest restriction or weight loss, but it can be used that way with appropriate context.
Ella sigue una dieta balanceada.
(She follows a balanced diet.)
Estoy haciendo una dieta para perder peso.
(I'm on a diet to lose weight.)
Régimen
'Régimen' carries more formal connotations than 'dieta'. It suggests a structured program or a set of rules about what one should eat. It is often used to refer to specific health-related diets prescribed by doctors or nutritionists.
Mi médico me puso en un régimen para reducir el colesterol.
(My doctor put me on a diet to reduce cholesterol.)
El régimen de alimentación que sigo es muy estricto.
(The eating regimen I follow is very strict.)
Summary
'Dieta' and 'régimen' both translate into English as 'diet', but carry different suggestions about the structure and restrictiveness of one's eating habits. 'Dieta' stands for the common term 'diet' without any particular restrictions, while 'régimen' implies a strict structured plan for eating or a medically advised diet.