This paper aims to identify changes in food group consumption that may improve both health and sustainability scores of low-scoring population subgroups. As a case study, we assessed the impacts of the diets of a representative sample of Dutch consumers (age 18–75 y, n = 1242). The health impact of their diets was assessed using the Dutch Healthy Diet-index (DHD) and the environmental impact by greenhouse gas emissions (GHGEs). As expected, a significant negative correlation was found between DHD and the GHGEs, indicating that health and sustainability can, to some extent, be improved in synergy with one another. Looking at population subgroups, (young) employed males were identified as an important target group (lowest DHD and highest GHGEs). Four food groups and energy were observed of which a reduced intake makes a diet healthier and more environmentally sustainable: meat, energy, cheese, snacks (cakes, pastry, biscuits, salted and fried snacks, potato chips), and alcohol. Besides, three food groups were observed of which an increased intake makes a diet healthier, but less environmentally sustainable when they do not replace other food groups: fruit, fish, and vegetables. Based on real-life differences in dietary patterns, four transition strategies were formulated that can raise the DHD and lower GHGEs: (I) Replacing snacks with fruit, especially between meals, (II) Replacing cheese with vegetables, during lunch as well as dinner, (III) Partly replacing meat with fish, (IV) Lowering the total energy intake, through reducing the consumption of alcoholic drinks. If deriving the highest environmental gain is the purpose of dietary adjustment, then halving the portions of meat consumed is a strategy (V). Actual unsustainable diet practices of specific subgroups require dedicated transition strategies. The study provides insights into the opportunities for improving both health and environmental sustainability scores of different population subgroups and underlines that these cannot be successfully achieved by adopting a single strategy.