What is good and bad cholesterol? Should you remove fat from your diet? And what about shellfish? Experts explain it all

High cholesterol can cause heart problems and strokes – but levels can creep up without showing any symptoms. This is why, if you’re over 40, you should be getting your cholesterol checked every five years. It’s a simple enough concept, but, like alcohol and other things that could be slowly, invisibly damaging our bodies, cholesterol can feel a little abstract, hovering in the background less urgently than everything in the foreground of a busy life.

It doesn’t help when myths are flying about online, such as eggs being unhealthy because they contain cholesterol. Or when some fringe scientists and proponents of low-carb and high-fat diets dramatically downplay cholesterol’s significance in heart disease – arguing that sugar is a bigger risk to our health, despite all the evidence to the contrary. Nor does it help us laypeople that there are so many different ways to present – and therefore interpret – cholesterol levels.

When your old knives no longer make the grade, should you buy British or Japanese, stainless steel or carbon steel, factory-made or handmade?

In Deptford, south-east London, Holly Loftus hand-crafts between 10 and 15 knives a month. The least expensive of these could be yours for £160, while the dearest might set you back as much as £580. What do you get for your money if you seriously splash out? Loftus, who was born in Ireland and is soft spoken and gently thoughtful, takes her time with this question. “It’s to do with how much time I’ve spent combining different steels,” she says, hesitantly. “Some of the knives involve a layering technique – people know it as damascus steel – which creates a pattern on the blade. It takes a long time. There’s a lot of folding and cutting and hammering.”

Such a knife is likely to be with its owner for a good while – perhaps for ever. “I’m lucky,” she continues. “The people who buy my knives have a strong sense of what they’re getting. It’s not going to be the same as an off-the-shelf, factory-made knife. They know they’re going to have to look after it.”

On straight line missions, YouTubers jump fences, wade through rivers, and almost die in peat bogs. It’s completely pointless – and weirdly beautiful

Spending too much time on YouTube can be a dangerous game for men my age. Algorithmic gyres can pull you rightwards – towards misogynistic extremes and away from the parts of the internet that build connections and foster consensus.

Thankfully the rabbit hole I fell down led me – in a perfectly straight line – towards a renewed sense of childlike adventure.

The long-running series in which readers answer other readers’ questions on subjects ranging from trivial flights of fancy to profound scientific and philosophical concepts

Why do posh people wear pullovers casually draped over their shoulders? Jane, by email

Send new questions to nq@theguardian.com .

The Tories are trailing third in the polls and look set for local election disaster. If Reform is the answer, she may have to go

Kemi Badenoch may only be four months into her leadership, but already Westminster is talking about her successor. Nigel Farage declared over the weekend that the Conservative party leader would be “lucky to survive past June ”. Of course, he would say that. The Reform UK leader has a personal interest in Tory misfortune. But more concerning for Badenoch is that some in her own party are starting to ask if she’ll still be leader at the next election.

Her problems are piling up. The Tories regularly come third in national polls behind Reform and Labour. There is little money to go around ( despite a spurt in Tory donations late last year ) and redundancies at Conservative campaign headquarters (CCHQ) are seen as inevitable. Badenoch’s performances at prime minister’s questions are regularly criticised among Tory MPs for being too scatter-gun and missing open goals. The May local elections will be the first electoral test of her leadership – and CCHQ sources are attempting some serious expectation management as they warn of losses.

Katy Balls is the Spectator’s political editor

Evidence is mounting to explain how birds use the Earth’s magnetic field to help fly thousands of miles with unerring accuracy – a discovery that may help advance quantum technology

To the seasoned ear, the trilling of chiffchaffs and wheatears is as sure a sign of spring as the first defiant crocuses. By March, these birds have started to return from their winter breaks, navigating their way home to breeding grounds thousands of kilometres away – some species returning to home territory with centimetre precision . Although the idea of migration often conjures up striking visions of vast flocks of geese and murmurations of starlings, “the majority,” says Miriam Liedvogel , director of the Institute of Avian Research (IAR) in Germany, “migrate at night and by themselves, so they have no one to follow.”

Liedvogel has had a fascination with birds since childhood, and often wondered how they navigate these lengthy migrations. She is not alone, with even Aristotle pondering the mystery and mistakenly concluding that redstarts change into robins over the winter. As Liedvogel points out, migration behaviour is varied and much remains unknown, but we now have enough data on bird behaviour to rule out species transmogrification, among other theories. Studies have revealed that 95% of migrating birds travel at night, alone, and without parental guidance, so the behaviour must be partly inherited. These birds use the Earth’s magnetic field to find their way, and it is likely that at least part of the biological mechanism that allows them to do this can be explained through quantum mechanics.

Israel continues to batter territory in renewed offensive as Palestinian officials say death toll of war has passed 50,000

Malnutrition is spreading in Gaza, medics and aid workers in the devastated Palestinian territory are warning, as a total Israeli blockade of all supplies enters its fourth week.

There has been no sign that Israel will open entry points to allow essential aid to flow or ease the new offensive in Gaza , which started on Tuesday with a wave of airstrikes that killed 400 people, mostly civilians , ending two months of relative calm. On Sunday, Palestinian officials said the total death toll from nearly 18 months of conflict had passed 50,000.

• The two clubs clash again in the third of four meetings
• Any thoughts? You can email Daniel with them

Manchester City (4-3-3): Keating; Casparij, Prior, Aleixandri, Layzell; Hasegawa, Roord, Coombs; Kerolin, Miedema. Park. Subs: Annets, Startup, Ouahabi, Fowler, Wienroither, Oyama, Murphy, Davies.

Chelsea (4-2-3-1): Hampton; Lawrence, Bright, Bronze, Charles; Jean-Francois, Kaptein; James, Hamano, Kaneryd; Beever-Jones. Subs: Spencer, Bjorn, Baltimore, Walsh, Cuthbert, Macario, Nushken, Fishel, Ramirez.

The governor dismissed an ex-judge studying the death penalty in the state and failed to heed a leading voice on the matter. It’s no surprise

On Wednesday, 19 March, Arizona executed Aaron Gunches by lethal injection . As ABC News reports , he was put to death for “kidnapping and killing 40-year-old Ted Price by shooting him four times in the Arizona desert”.

Gunches’s case was unusual in many ways, not least that he stopped his legal appeals and volunteered to be executed, then changed his mind before changing it again. His execution was scheduled to be carried out almost two years ago. It was put on hold when the Arizona governor, Katie Hobbs, commissioned an independent review of the state’s death penalty procedures after a series of botched executions .