The ketogenic diet is everywhere right now. If you have been anywhere near social media in recent year, you will be all too aware of the hype surrounding keto and the strength of feeling it engenders, both for and against.
For some people, it is the only way to lose weight; for others, it’s just another tool to create a calorie deficit.
But what is the ketogenic diet? How does it work? What are the benefits and drawbacks of following a keto diet? And is the ketogenic diet the best way to lose weight?
In this second instalment in our Diets Reviewed series, we’re putting the claims under the spotlight and sharing everything you need to know about keto.
What is a Ketogenic Diet?
The keto diet involves a process known as ‘ketosis’, which happens when your body doesn’t have carbohydrates to use as energy. Stone-age man would have been unlikely to have constant access to grains, fruits and other carb sources. Instead, the human body has adapted to burn fat and produce ‘ketones’ from fat (both stored and dietary), which it uses for energy.
Once you enter ketosis, your body undergoes biological adaptations, such as reduced insulin levels and increased fat breakdown. And it is these ketones that lend the diet its hallmarks. For instance, the ketone ‘acetone’ is partially expelled through your breath, responsible for the famous keto halitosis.
In its strictest form, the keto diet is a very low-carb, high-fat diet. What you may not know is that keto is not just low-carb; it’s also relatively low-protein. This is because the body can break down protein and convert it into glucose via a process known as glucogenesis. And as soon as the body starts using glucose as a fuel source, you’re no longer in ketosis. So, if you’re thinking about going keto, reconsider that glass of wine on the weekend.
What can you eat on a ketogenic diet?
Many proponents of the keto diet claim that you can eat high-fat, low-carb foods to your heart’s content without the need to track your calorie intake. This includes fatty meat and fish, eggs, avocado, nuts, cheese and a limited range of non-starchy vegetables, like spinach and cucumber.
The keto diet is therefore also pretty restrictive. You won’t find any carbs, like grains, starchy vegetables or high-fructose fruit here, so say goodbye to pasta, bread and your favourite sweet treats. Some low-sugar fruits like berries are allowed in very low quantities, but there certainly won’t be room for a morning smoothie.
Here’s an overview of what you can and can’t eat on the keto diet:
| Permitted | Amount | Not Permitted/ Restricted | Amount |
|---|---|---|---|
| Seafood | Unlimited | Potatoes | None |
| Cheese | Unlimited | Sweet potatoes | None |
| Avocado | Unlimited | Rice | None |
| Meat and poultry | Limited | Honey, maple syrup or any other kind of sugar | None |
| Eggs | Unlimited | Fruit juice | None |
| Full-fat Greek yoghurt | Limited | Sweetened yoghurt | None |
| Full-fat cream | Unlimited | Baked goods | None |
| Dark chocolate and cocoa powder | Limited | Bread | None |
| Broccoli | Limited | Pasta | None |
| Cauliflower | Limited | Banana | None |
| Green beans | Limited | Raisins | None |
| Bell peppers | Limited | Dates | None |
| Courgette/ zucchini | Limited | Mango | None |
| Spinach | Limited | Pear | None |
| Nuts | Unlimited | Sweetcorn | None |
| Blackberries | Limited | Beetroots | None |
| Blueberries | Limited | Legumes | Some |
| Raspberries | Limited | Beans | Some |
| Strawberries | Limited | Grapes | None |
| Olive oil | Unlimited | Tomato sauces | None |
| – | – | Oats | None |
| – | – | Couscous | None |
| – | – | Alcohol | None |
Ketogenic diet: The pros
1. It has some health benefits.
Keto ‘experts’ claim that ketosis increases fat burning, reduces hunger and boosts metabolic rate [1]. Some studies also show that it may improve markers for weight loss, diabetes and epilepsy [2], [3],[4].
2. It could improve Alzheimer’s.
Evidence indicates keto could be beneficial for certain cancers, Alzheimer’s disease, and multiple other disease states [5]. However, further research is needed to confirm the long-term safety and efficacy of this nutritional approach.
3. You might feel less hungry.
Keto appears to affect hunger signalling positively, so if you like high-fat foods such as eggs, nuts, avocado, and fatty meats, keto could improve your dietary adherence. However, a diet full of healthy grains, starchy carbs and lots of vegetables can be just as satiating, without the restriction.
4. You might not have to count calories (all the time).
If you’re someone that hates counting calories, the strict framework governing what you can and can’t eat during a keto diet may make it easier to stick to a calorie goal.
Ketogenic diet: The cons
1. It’s restrictive.
While there’s a lot you can eat on the keto diet, your food choices will likely be much less varied. The keto might be perfect if you’re happy eating the same meals day-in, day-out. However, if you believe that variety is the spice of life, going keto might not be the right fit.
2. It’s high in saturated fats.
Many of the ‘permitted’ foods are high in saturated fat (think cheese, fatty meats and full-fat dairy), which can increase your risk of developing high cholesterol [6]. Current guidelines recommend that no more than 10% of your daily fat intake should come from saturated sources, and prioritising mono- and polyunsaturated sources, such as nuts, avocado, olive oil, and so on, will provide far more health benefits [7], [8].
In addition, a high-fat diet is naturally more calorific if you don’t control for energy intake. At 9 kCal per gram (compared to 4 kCal per gram for carbohydrates and fats), the calorie count can soon add up. Energy balance is always the non-negotiable requirement for fat loss.
3. It could quickly become boring.
Restrictive diets spell trouble as soon as you even think the words ‘social occasion’. A diet is only as effective as the extent to which it fits your lifestyle. Going keto could mean you unnecessarily restrict your food and social choices when other strategies might be just as effective without the negative trade-offs.
4. Reduced fibre intake is common with keto.
Endless research shows that fibre is a vital dietary component that supports digestive health, lowers cholesterol, improves mental health, as well as multiple other benefits [9]. Because keto restricts key sources of fibre, such as grains, legumes, starchy vegetables, and some fruits, it’s much harder to obtain all the fibre you need.
Keto diets are often lacking in sources of fibre that support health.
Keto claims examined
There are many claims about the efficacy of the keto diet, ranging from the relatively sensible to the outright outrageous! But do they stack up against the science?
1. Carbs cause fat gain, so removing them will result in weight loss, regardless of energy balance.
Keto enthusiasts believe that removing carbs from the diet is essential for fat loss due to their effect on insulin, which gets a bad rap because it is a ‘storage’ hormone. Insulin allows us to circulate and store carbohydrates in muscle cells as glycogen, which is crucial for high-intensity exercise.
However, insulin doesn’t cause fat gain independently of energy balance, and both high-carb and high-fat diets produce similar rates of fat loss when calories are equal [10]. The evidence also indicates that insulin sensitivity (our ability to store and uptake glycogen from muscle cells) improves with weight loss, even on high-carb diets [11],[12]. So, any diet that allows you to lose weight will boost your insulin sensitivity, regardless of the precise ratio of fats to carbohydrates in our diets.
2. The keto diet increases metabolic rate and, therefore, daily energy expenditure. This means you can lose weight without decreasing your calorie intake.
A landmark 2018 study appeared to show that lowering dietary carbohydrate intake increased energy expenditure during weight-loss maintenance [13]. Hunger signalling, due to reduced levels of the hormone ghrelin, also appeared to improve. As a result, some in the fitness sphere concluded that calorie balance no longer mattered and that this increase in metabolic rate would magically offset all the additional calories from high-fat, high-calorie foods.
However, multiple papers demonstrate that when calorie and protein intake are the same, calorie burn remains consistent in both low- and high-carb diets [14]. In addition, keto may even be less likely to increase metabolic rate as it requires low protein intake, which has the highest thermic effect of food or ‘TEF’. TEF is a small but significant contributor to total daily energy expenditure (TDEE) by increasing your internal body temperature to digest food. So, in either sense, the claim that keto increases metabolic rate does not stack up against the science.
With a calorie deficit in place and sufficient protein intake, you will lose weight whether you use a low-carb or low-fat approach.
3. You won’t feel hungry on a keto diet.
It’s true that you shouldn’t feel excessively hungry during a fat loss diet. However, even with the best nutritional strategy, restricting your energy intake means that hunger is sometimes inevitable.
Keto advocates argue that the keto diet reduces hunger, and the research indicates that this could be true. Analysis shows that overweight and obese people see success with the keto diet due to its appetite-lowering effects [15]. In contrast, mainstream fat loss research shows that weight-loss diets nearly always increase appetite [16]. However, the mechanism behind this weight loss is likely because keto allows adherents to reduce their overall calorie intake [17], [18]. In addition, keto typically takes highly palatable, highly processed foods off the menu, replacing them with satiating foods, such as nuts, proteins and some fruits and vegetables [19], [20], [21]. The crucial takeaway is that keto may allow you to achieve a negative energy balance while feeling a little less hungry.
The Keto Diet Demystified
While the keto diet has some health benefits, this is primarily because it reduces the intake of highly processed foods and replaces them with unprocessed, high-quality sources. It’s no wonder, then, that proponents claim to feel more energised, less hungry and better able to adhere to their diet.
However, its highly restrictive nature means that the benefits mostly don’t outweigh the cons, especially when we look at health in the round. So, if the keto diet works for you, great! But, for most people, there are less restrictive alternatives that provide just as many health benefits while offering far more flexibility.
Key Takeaways
- A ketogenic diet is a very low-carb, high-fat, moderate-protein diet, typically comprising fatty cuts of meat and fish, eggs, oils, avocados, nuts, and non-starchy vegetables like spinach and cucumber.
- The metabolic state of ketosis is the central concept behind the keto diet.
- Keto zealots claim that you burn fat without decreasing your calorie intake by going ultra-low-carb.
- A common claim is that keto increases metabolic rate, which science does not support.
- Limited research indicates that the keto diet may improve hunger, although this could be due to general dietary changes.
- Severely restricting carbohydrates does not appear to improve rates of fat loss or metabolic rate.
- Keto provides strict rules and structure, which may be beneficial if counting calories isn’t your thing.
- However, keto proponents often encourage high saturated fat and low-fibre intakes, increasing the risk of major health issues.
- The success of the keto diet lies in its ability to create a calorie deficit, which we can achieve through multiple other, less restrictive means.