Dietary recommendations are generally sound and assume conditions that a substantial proportion of households do not have.
The cost gradient
Analyses of food cost consistently find that energy-dense foods are cheaper per calorie than nutrient-dense ones.
Which means a constrained budget optimising for calories per pound arrives at a different diet from one optimising for nutrition.
The gap has widened over time in several countries that track it.
Time
Cooking from ingredients requires time, and time is unequally distributed.
Which means households with long working hours, multiple jobs or caring responsibilities face a genuine constraint that advice to cook from scratch does not address.
Batch cooking addresses it partially and requires an initial block of time and storage capacity.
Equipment and storage
Cooking requires a functioning cooker, pans and storage.
Which is not universal, and temporary accommodation frequently lacks cooking facilities entirely.
Freezer capacity determines whether batch cooking and buying in quantity are possible.
Access
Distance to shops selling fresh food, and transport to reach them, vary substantially.
Which has been mapped in several countries, identifying areas with limited access to affordable fresh food.
Carrying capacity matters where shopping is done on foot or by public transport, which limits bulk purchase.
Risk
Trying a new food that a household does not eat wastes money if it is rejected.
Which makes experimentation a luxury, and it explains why constrained households buy what is reliably eaten.
Food waste carries a proportionally larger cost on a smaller budget.
What actually works within constraints
Frozen vegetables and fruit, which are nutritionally comparable and cheaper with no waste.
Tinned pulses and fish, which are inexpensive nutrient-dense and shelf-stable.
Dried pulses, cheaper again where cooking time and fuel cost permit.
Own-brand equivalents, which are frequently identical products.
Eggs, oats and root vegetables, which are consistently among the cheapest sources of what guidance recommends.
Fuel poverty
Cooking costs energy, and energy costs affect what is practical.
Which means slow cooking, oven use and long-boiling foods carry a cost that is not obvious.
Advice recommending them to households in fuel poverty is not workable.
Support
Food assistance schemes, free school meals, and vouchers for specific foods exist in many countries and are consistently underclaimed.
Which means checking entitlement is worthwhile, and free advice services can check comprehensively.
Anyone struggling to afford food should contact local support services, which exist in most areas and include emergency provision.
Food environment
What is available and promoted where people shop affects what is bought measurably.
Which is why regulation of promotion placement and of advertising has been introduced in several jurisdictions.
Evaluations of these measures have found modest effects, which is unsurprising given the size of the intervention relative to the environment.
Cooking skills
Frequently identified as a barrier and easier to address than cost.
Which community cooking programmes attempt, with modest and generally positive evaluation results.
The evidence is stronger where programmes address cost and access alongside skills rather than skills alone.
Nutrition rather than weight
Advice framed around weight performs poorly and produces documented harms including disordered eating.
Which is why framing around nutritional adequacy and around specific behaviours works better.
Adding foods rather than removing them is generally more sustainable and less likely to produce a restriction cycle.
Food insecurity
Measured by whether households can reliably access sufficient food, and rates have risen in several wealthy countries.
Which has effects on physical and mental health that are documented.
Emergency food provision has expanded to meet it and is explicitly not a solution, as the organisations providing it consistently state.
What actually helps
Income is the main determinant, which means income support measures affect diet more than any advice does.
Targeted schemes providing specific foods have reasonable evidence where take-up is good.
Anyone with a health condition affecting diet should get advice from a dietitian, and referral routes exist through primary care.
Portion and packaging
Smaller pack sizes frequently cost more per unit, which penalises households buying small quantities.
Which affects people with limited storage, limited cash on hand or limited carrying capacity.
Multi-buy promotions require money now to save later, which is not available to everyone.
Supplements
Recommended in specific circumstances rather than generally, including for particular vitamins in particular populations and seasons.
Which is worth checking against local public health advice, since recommendations differ by latitude and by diet.
Broad supplementation without indication has not shown benefit in large trials.
Children
School food provision reaches children whose diet is otherwise constrained.
Which makes eligibility rules and holiday provision consequential.
Take-up of free entitlements is below eligibility in most systems, and registration is worth checking.
Batch and freeze
Cooking once for several meals reduces both cost and time per meal.
Which requires freezer space and a block of time, and where both exist it is the highest-return change available.