The Keto Diet, Honestly: The Ups, the Downs and What to Watch For
Few eating plans inspire such strong feelings as keto. Fans swear by it, critics warn against it, and chances are you have heard a story from someone who lost weight quickly. This is the first in our series on popular ways of eating, and we will walk through the ups, the downs and what to keep in mind, so you can decide with a clear head whether it suits you.
What keto is
A ketogenic diet is very low in carbohydrates, high in fat and moderate in protein. Carbohydrate intake is often kept to somewhere around 20 to 50 grams a day, which cuts out most bread, pasta, rice, sugar, fruit and starchy vegetables. With so little carbohydrate available, your body shifts to burning fat and making ketones for energy, a state called ketosis.
The ups and the downs
| What reviews report as upsides | What reviews report as downsides |
|---|---|
| Short-term weight loss, including reductions in body fat and waist size | Long-term results are unclear and do not appear to beat other diets |
| Triglycerides often go down and HDL (“good”) cholesterol often goes up | LDL (“bad”) cholesterol often goes up, sometimes by a meaningful amount |
| Some improvement in selected blood sugar and metabolic measures | “Keto flu” in the first days or weeks: headache, fatigue, dizziness, nausea, constipation |
| A clear set of rules can feel simple to follow | Very restrictive, and hard for many people to sustain |
| Concerns in long-term use include nutrient gaps and, in some people, kidney stones and fatty liver |
Can keto help you lose weight?
Good news first: reviews of the research generally agree that keto can produce weight loss in the short term. They also agree that, over the long run, it does not appear to offer a significant advantage over other dietary strategies. In other words, it can work for you, but it is not magic. That matches what we saw with intermittent fasting: many approaches work when you can stay with them, so the best plan is often the one you enjoy enough to keep.
Things to keep in mind
- Cholesterol. If your LDL rises on keto, that matters, especially if you already have high cholesterol or heart disease in your family. Ask your doctor to check your blood fats before and after you start.
- Medications. If you take medication for diabetes or blood pressure, carbohydrate restriction can change how much you need. Please do not adjust anything on your own.
- Fiber and variety. Cutting carbohydrates can cut fiber, fruit and many vegetables. Non-starchy vegetables, nuts and seeds help fill the gap, and constipation is a common complaint.
- Fluids and electrolytes. Some of the early “keto flu” symptoms ease with enough fluids and minerals such as salt, but ask a professional what is right for you.
- The kind of fat. A plan built on processed meats and a lot of saturated fat is not the same as one built on fish, olive oil, nuts and vegetables.
- Protein. Keto is moderate in protein, which is worth checking against our guide to how much protein you need.
- Coming off it. Weight lost on any restrictive diet can return if the old pattern does, so plan ahead for how you will eat afterward.
Who should talk to a doctor first
Please check in with a doctor or registered dietitian before trying keto if you are pregnant or breastfeeding, have diabetes, kidney or liver disease, a history of pancreatitis or gallbladder problems, high cholesterol, or any history of disordered eating, or if you are under 18.
Final thoughts
Keto can help some people lose weight in the short term, and some of its blood markers move in a good direction. It also carries real trade-offs, from cholesterol to nutrient gaps, and its long-term record is unclear. If you try it, do it with medical guidance and a plan for how to eat afterward. And if it is not for you, that is perfectly fine: there are other well-studied ways to eat well, and we will explore several of them in this series.
Sources
- Advantages and disadvantages of the ketogenic diet: a review article. PMC7480775
- Ketogenic diet intervention for obesity weight loss: a narrative review, challenges, and open questions. PMC11890254
This article describes research and is not medical advice. Talk with your doctor or a registered dietitian before starting a ketogenic diet. See our Medical Disclaimer.
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