Sophia Wanjiku is up at 4 am. She doesn’t have a choice.
By the time Nairobi’s streets begin to fill, she is already deep into her first batch of mandazis, standing over a hot jiko, watching oil shimmer in an aluminium pan. Every litre of that oil costs her more than KSh358. And she is not throwing a single drop away before it is absolutely finished.
This is not a story about bad habits. It is a story about what economic pressure does to people who are already running on empty — and about a government that has left them to figure out the health consequences entirely on their own.
Cooking oil prices in Kenya have climbed steadily. Data from the Kenya National Bureau of Statistics shows the average retail price of one litre of cooking salad oil rose 3.3 per cent year-on-year, from KSh347.17 to KSh358.63. That number sounds modest until you are a mandazi vendor calculating costs before sunrise, or a household mother stretching a budget across a week of meals. Then it hits differently.
So people reuse oil. They store it after frying, pour it back into the pan the next morning, and sometimes top it up with a splash of fresh oil to keep things going. This is not ignorance. This is rational behaviour under financial stress. But the chemistry happening inside that pan is something most people frying mandazis or chips have never been told about — and that silence is the real scandal here.
When cooking oil is exposed to heat, three chemical processes begin: oxidation, where oxygen attacks the oil’s molecular structure; hydrolysis, where moisture from food breaks down fat molecules; and polymerisation, where degraded compounds combine into larger, heavier substances. Dr Sheila Kilonzi, a food science and nutrition lecturer at JKUAT, is clear about what this means — the oil you are frying in today is chemically different from the oil you bought. Repeated heating accelerates that transformation, producing compounds including peroxides, aldehydes and free fatty acids. One of those compounds, acrolein, irritates the eyes and respiratory tract. Another, benzene, is a recognised carcinogen linked to bone marrow damage and an increased risk of blood cancers.
Toxicologist Joseph Bundotich puts it plainly: cooking oil does not simply lose flavour after repeated heating — it changes chemically. The rate of change depends on the oil type, the temperature, how long it is heated, and the moisture content of whatever is being fried. Sunflower and soybean oils, which dominate Kenyan kitchens because of their price point, are polyunsaturated and among the most vulnerable to oxidative breakdown. The affordable option is, structurally, the most fragile one.
Toxicologist and pharmacologist Dr Mercy Maina wants to be precise about the risk, because nuance matters here. Eating food fried in reused oil once is not going to hospitalise you. The danger is cumulative — daily consumption of food prepared in heavily reused oil, over months and years. She compares it to cigarette smoke: no single exposure destroys you, but repeated exposure builds a burden your body eventually cannot absorb. For Kenyans who eat deep-fried street food as a daily staple, not an occasional treat, that accumulation is not hypothetical. It is already happening.
The practice of mixing fresh oil with old oil to extend its life is widespread among vendors and households alike. Experts are unanimous that this changes nothing chemically meaningful. Adding fresh oil to degraded oil does not reverse the breakdown that has already occurred — it dilutes it, but it does not restore it. Filtering oil to remove food particles helps with visible impurities, but the toxic compounds that have built up during repeated heating remain. The oil looks cleaner. It is not safer.
Here is where the government’s failure becomes impossible to ignore. The Kenya Bureau of Standards sets requirements for cooking oil manufacturers — production quality, vitamin A fortification — but KEBS has confirmed there is currently no published national standard specifying how many times cooking oil can safely be reused, either in homes or commercial food businesses. None. KEBS says it is working toward guidance based on Total Polar Content, a scientific measure of how degraded oil has become, but that guidance does not yet exist in any enforceable or publicly accessible form. That means Wanjiku, and every other small food vendor and household cook across this country, is making a health decision in a complete information vacuum.
Experts are not naive about the economics. Telling people to discard oil after one use is not a policy — it is a luxury that most Kenyans cannot afford. What food scientists and dieticians recommend instead is practical and achievable: avoid heating oil to the smoking point, reduce how many times the same oil is reheated, store used oil properly in a cool dark place, and shift toward boiling, steaming or baking where possible to reduce dependence on deep-frying altogether. These are not radical suggestions. They are harm reduction measures for a population navigating real financial constraints.
But harm reduction only works when people know there is harm to reduce. Right now, the gap between what food scientists know and what street vendors and households are told is vast, deliberate in its neglect, and dangerous in its consequences. Rising food prices are forcing micro-businesses and families into practices that carry long-term health risks. The government knows this. The science is not new. And yet the regulatory framework that should protect ordinary Kenyans from compounding poverty with preventable illness simply does not exist.
Wanjiku will be back at her jiko tomorrow at 4 am. The oil in her pan will have been used before. The question of how many times is one she has to answer alone — because no one in authority has seen fit to answer it for her.
