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
A2This 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
B1Régimen 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.