The ketogenic diet has been praised, criticised, mythologised and misunderstood in equal measure. At its core, keto is simply a metabolic shift — a change in the body’s preferred energy source from glucose to fat-derived ketones. For some people, this shift creates sharper energy, easier fat loss and more stable appetite. For others, it feels restrictive, unsustainable or too extreme. Understanding how keto works physiologically makes it much easier to evaluate whether it’s a smart choice for your goals.

What Keto Actually Is

Keto is a high-fat, moderate-protein and very low-carbohydrate diet designed to push the body into a state called nutritional ketosis. In ketosis, the liver converts fats into molecules known as ketones, which can power the brain, muscles and organs when glucose is limited. Humans are metabolically flexible, but most modern diets rely heavily on carbohydrates. Keto flips that ratio, encouraging the body to burn stored fat more consistently.

How the Metabolic Switch Happens

In the first few days of keto, glycogen stores (the body’s short-term carbohydrate supply) begin to dwindle. When that happens, insulin levels fall and the body increases its reliance on fat for fuel. The liver begins producing ketones, which cross the blood–brain barrier and provide a steady energy source for the brain.

This transition isn’t immediate. Many people experience a lag — often called the “keto flu” — where energy dips as the body adjusts to using ketones efficiently. Hydration, electrolytes and gradual carbohydrate reduction can soften the transition, but the adaptation still takes time. Once the body becomes “fat-adapted,” energy often feels more stable because ketones are released in a slow, steady stream rather than fluctuating like glucose.

Why Keto Can Lead to Fat Loss

Keto influences weight loss through several mechanisms beyond simply cutting calories:

• Lower insulin levels make it easier for the body to access stored fat.
• Appetite often decreases because ketones naturally blunt hunger hormones.
• Blood sugar becomes more stable, reducing energy crashes and cravings.
• The loss of glycogen and water weight can create an immediate early change, which is motivating for some people.

It’s not a magic diet, but it is a metabolically coherent one, especially for people who struggle with blood sugar swings or constant hunger.

The Energy “Explosion” After Adaptation

Once the body becomes ketone-efficient — which can take anywhere from two to six weeks — many people report:

• smoother, more even energy
• less dependence on snacking
• improved mental clarity (“keto focus”)
• fewer afternoon slumps

This is because ketones provide a remarkably stable fuel source. There are no dramatic peaks and troughs, and the brain can run on ketones extremely well once adapted.

Potential Health Benefits Backed by Research

Keto has been studied for decades, originally for its therapeutic effects on epilepsy. More recent research explores its benefits for:

• improved insulin sensitivity
• reduced triglycerides and improved HDL cholesterol
• reduced inflammation in some individuals
• appetite regulation
• metabolic flexibility

For people with prediabetes, insulin resistance or PCOS, stabilising blood sugar through keto can be particularly helpful.

Who Keto Is Suitable For

Keto can be appropriate for:

• individuals with blood sugar instability
• people who feel better on higher-fat diets
• those wanting appetite control
• individuals with neurological conditions (under medical supervision)

It’s not ideal for:

• people with a history of restrictive eating
• pregnant or breastfeeding women
• athletes relying on explosive, high-intensity performance
• individuals who feel unwell on very low carb diets

Keto is a tool — not a universal solution.

Is the Keto Diet Sustainable Long-Term?

Sustainability depends entirely on lifestyle and personality. Some people thrive on structure and enjoy predictable meals with fewer cravings. Others find the restrictions impractical or socially limiting. Hybrid approaches such as cyclical keto, moderate low-carb eating or “ketonising” just one meal a day can offer some metabolic benefits without full commitment.

In practice, keto tends to be most sustainable when:

• meals include plenty of fibre-rich, non-starchy vegetables
• electrolytes are prioritised
• whole foods, not processed keto snacks, form the base of the diet
• protein intake is kept moderate, not excessive

There is no requirement for keto to be lifelong. Many people use it strategically for a few months to reset cravings or stabilise blood sugar, then transition to a balanced maintenance approach.

The Bottom Line

Keto works because it changes the body’s primary fuel source, lowers insulin and trains metabolism to rely on fat and ketones. For some, this creates steady energy, easier fat loss and fewer cravings. For others, the restrictions outweigh the benefits. Like any dietary pattern, its success depends on the individual — their physiology, preferences and lifestyle. Understanding the underlying mechanisms makes it far easier to decide whether keto is a tool worth using.