How to lose weight: keto, fasting, and three more diets tested by research

## Introduction

Fat is the problem. Carbohydrates are the problem. You simply need to count calories, eat only protein—or perhaps eat only on even-numbered days of the month?

There are hundreds of suggestions for the best diet to help you lose weight and keep it off. With all this excess information, it is hard to know what to do, which diet is most effective, and which one genuinely suits you.

Today we will review five common diets and examine how each works, how effective it is for losing weight and maintaining the loss, and who it may or may not suit, so that by the end of the video you can choose what fits you.

I am Dr. Elisheva, and here you will get clear, direct medical information about healthy living—what is proven and what is myth—so you can make informed decisions about your health.

## Diet 1: tracking and calorie counting

How does it work? As you guessed, you count calories. You set a daily calorie target and try not to exceed it. Various apps do this directly, while some programs use a points system that also accounts for other factors.

It is based on a correct principle: when, over time, we take in less energy than we expend, we lose weight. But calorie counting is only one way to create that deficit; it is not a rule that must be followed to lose weight.

How effective is it? In structured programs that combine a calorie deficit, monitoring, and support, losing 5% to 10% of body weight is an achievable and medically meaningful goal. But there is no single percentage that applies to everyone. The result depends on the size of the deficit, the duration of the intervention, monitoring, and the ability to adhere. Self-monitoring itself is generally associated with better weight loss, probably because it makes eating more conscious.

What happens in the long term? As with every approach, some weight tends to return after the intervention ends. There is no single reliable number showing what percentage of people “succeed” after two years, because studies define success differently and include different levels of support. The more sustainable the tracking feels and the more ongoing support there is, the better the chance of maintaining the result.

The major advantage is flexibility. No food has to be forbidden; it is all a matter of quantity. This can suit someone who does not want to give up a particular food and would rather eat a small piece of cake than avoid it completely; someone who likes data, boundaries, and control; and someone able to keep tracking over time. It is a little like the obsessive friend who makes an Excel spreadsheet for every trip abroad: precise and fond of control.

The disadvantage is that tracking can be tiring, is harder when eating out, and does not necessarily teach you to choose nutritious food. You can meet a calorie target while still eating a diet low in fiber and vitamins. Not everyone is hungry on this kind of diet, but hunger can certainly make it difficult if you mainly choose foods that are not filling. It is also less suitable for people in whom tracking triggers obsessive behavior or who have a history of an eating disorder.

Most additional health benefits come from the weight loss itself. Food quality still matters because the number alone does not tell us what is on the plate.

In summary, a calorie deficit is the physiological basis of weight loss. Calorie counting gives you freedom to choose what you eat—but at the cost of doing the bookkeeping.

## Diet 2: keto and low-carbohydrate diets

It is important to distinguish between them. “Low carbohydrate” describes a broad family of diets, and keto is its more extreme form.

On a ketogenic diet, carbohydrates are severely restricted—usually to about 20 to 50 grams per day—a moderate amount of protein is eaten, and most energy comes from fat. For perspective, 20 grams of carbohydrate is less than half a cup of cooked rice, so this is a very substantial restriction.

When the carbohydrate supply is very low, the liver produces ketone bodies from fatty acids. These serve as an alternative energy source for some tissues. This state is called ketosis. In some mechanisms it resembles what happens during fasting, but here you are still eating and receiving energy, mainly from fat.

A high amount of protein does not automatically “knock you out” of ketosis. The body can produce glucose from some amino acids as needed, which is why classic keto generally includes moderate rather than unlimited protein. In practice, the response varies between people.

How effective is it? During the first months, weight loss may be slightly faster than with diets containing a balanced amount of carbohydrate, and some of the early loss is water due to depleted glycogen stores. But when weight-loss diets are compared over one to two years, research usually shows a very small or no meaningful difference in weight. In other words, keto does not bypass energy balance.

Its rules are clear, so it may suit people who find “I do not eat that” easier than negotiating every bite. Protein and fat increase fullness for some people, and reducing sweet foods can help limit cravings.

On the other hand, it is a restrictive diet that can be difficult at events, in restaurants, and in family life. Headache, fatigue, constipation, or nausea may occur at the beginning. If it is not planned well, it may be low in fiber, fruit, legumes, and other plant foods. And no—being in ketosis does not guarantee weight loss. You can be in ketosis while taking in more energy than you expend, and therefore you can also gain weight.

As for additional health benefits, a low-carbohydrate diet may lower triglycerides and improve glucose control for some people, especially those with type 2 diabetes. On the other hand, LDL may rise in some people, so it is important to examine the quality of the fat, not only the amount of carbohydrate.

Anyone taking diabetes medication—especially medication that can cause hypoglycemia or drugs from the SGLT2 family—as well as anyone with kidney disease, liver disease, pregnancy, or other medical conditions, needs professional adjustment and monitoring before starting.

In summary, a ketogenic diet may produce faster initial weight loss and reduce hunger and carbohydrate cravings for some people, but it is not metabolic magic. The challenge is to build it in a healthy way and be able to live with it over time.

## Diet 3: a high-protein diet

There is no single agreed definition of a high-protein diet. Studies sometimes use about 25% to 30% of calories from protein or set a daily target according to body weight.

Why might it help? Protein tends to be filling, and the body expends more energy digesting and processing it: roughly 20% to 30% of the energy in protein, compared with about 5% to 10% for carbohydrate and about 0% to 3% for fat. Protein also helps preserve lean body mass during weight loss, especially when combined with resistance training.

How effective is it? Compared with diets containing less protein, studies show a small to moderate average advantage in weight and fat loss, not a dramatic gap. The benefit for preserving muscle mass may be important even when the difference on the scale is small. Here too, there is no good basis for saying that a fixed percentage of people maintain their weight after two years. The long-term advantage mainly depends on the ability to maintain the protein intake and an eating pattern that fits real life.

The major advantage is fullness and better preservation of muscle mass. This approach can be especially suitable for people whose main obstacle is hunger, older adults who want to preserve muscle, and those willing to include resistance training.

The disadvantage is that if “high protein” becomes “only protein,” it can push fruit, legumes, whole grains, and fiber sources off the plate. It can also be followed by vegetarians or vegans, but may require more attention to planning and variety. Anyone with kidney disease that requires protein restriction needs an individualized plan.

The main additional health benefit is preserving muscle mass, which supports strength, function, and independence throughout life.

In summary, a high-protein diet can make you less hungry and help preserve muscle mass, but it should not become a diet made solely of protein.

## Diet 4: intermittent fasting

Intermittent fasting mainly restricts when you eat. The best-known method is 16:8—an eight-hour eating window—but there is also 5:2, in which food intake is greatly reduced on two days per week, and alternate-day fasting.

During the fasting hours, insulin levels gradually decrease, the body uses more glycogen and fat, and in practice many people reduce calories simply because they have fewer hours and opportunities to eat. This does not mean that every fasting window creates deep ketosis, and it certainly does not mean that you can eat without limits during the eating window.

How effective is it? Overall, intermittent fasting produces modest weight loss and is generally similar to continuous calorie restriction. In one large meta-analysis, only alternate-day fasting showed a small advantage over continuous restriction, and it is unclear whether this has a meaningful long-term benefit. There is currently no evidence that 16:8 maintains weight better than calorie reduction itself.

The advantage is simplicity: one clear rule instead of calculating every meal. The window can be adapted to your routine, and it may especially help people whose main problem is snacking or eating late at night. It is like the friend who says, “I do not want to know what is on the plate—only what time we agreed on.”

The disadvantage is hunger during fasting hours, difficulty around social events or shifts, and a risk of overeating during the eating window for some people. It is less suitable for anyone with a history of an eating disorder, while pregnancy, diabetes, or medication that affects blood glucose requires an individualized assessment.

Regarding additional health benefits, there is evidence of improved glucose and lipid measures in certain populations, but it is unclear how much results from meal timing and how much from weight loss. Claims about autophagy, concentration, or “resting the digestive system” are interesting, but human clinical evidence is still insufficient to promise a special benefit.

I have a full video about intermittent fasting in which I go deeper into what happens in the body during fasting, autophagy, metabolic health, and who the method may or may not suit. I will put a link at the end of the video.

In summary, intermittent fasting is mainly a way to organize eating and reduce opportunities to snack. It can work very well if the hours fit your life, but it is not necessarily better than ordinary calorie restriction.

## Diet 5: the Mediterranean diet

The Mediterranean diet is a balanced eating pattern that emphasizes vegetables, fruit, nuts, seeds, legumes, whole grains, olive oil, and fish, with less processed meat, ultra-processed food, and sweets.

Foods rich in fiber, protein, and unsaturated fat can increase fullness and improve metabolic measures. But this is not necessarily a weight-loss diet. To lose weight, you still need to create an energy deficit over time, for example by paying attention to quantities.

How effective is it? When a Mediterranean diet includes energy restriction and behavioral support, it can produce meaningful weight loss similar to other diets. There is no good basis for saying that it is always slower or that half the people following it maintain their weight. Its major long-term advantage is not a magical “success rate,” but a flexible, nutritious pattern that is relatively easy to integrate into life.

It suits people who want guiding principles rather than a list of prohibitions, families, people who eat out, and the Israeli kitchen. It is like the cousin who hosts everyone: she does not count every olive for you, but makes sure that most of what is on the table is genuinely food.

The disadvantage is that its flexibility may feel vague to someone who needs clear rules. Olive oil, tahini, and nuts are nutritious but energy-dense, so you may fail to lose weight—or even gain it—if portions are large.

This is where the strongest evidence for additional health benefits lies among the five approaches: reduced risk of cardiovascular events in high-risk populations and improvements in some lipid, blood pressure, and glucose-control measures.

In summary, the Mediterranean diet is less a “weight-loss campaign” and more an operating system for healthy living. When weight loss is the goal, attention to quantities is added as well.

## How to choose the diet that suits you

We have discussed five approaches to weight loss. All of them can work, but studies always compare group averages; within every group, some people lose more, some lose less, and some do not lose weight at all. The best diet for you is one that creates an energy deficit, provides the nutrients you need, and can be continued over time.

Ask yourself:

- What is easier for me to limit: quantities, types of food, or eating hours? - Do I need precise numbers and clear rules, or would flexibility help me adhere? - What happens when I am hungry: do I adapt, or compensate later by overeating? - Can I get enough protein, fiber, fruit, vegetables, and essential nutrients with this approach? - Does it work at home, at work, on weekends, and when I eat out? - Most importantly, can I imagine myself eating this way a year from now?

And do not forget: nutrition is only part of the picture. Sleep, stress, physical activity, smoking, and alcohol also affect health and the ability to maintain weight.

If you have diabetes, kidney or liver disease, are pregnant, take medication that affects blood glucose, or have a history of an eating disorder, do not choose an extreme diet based only on a video. Adapt it with a professional.

One problem with diets is that we call them diets: we follow them for a limited time, stop, and go backward. Think less about a “diet” and more about a change you can live with.

If intermittent fasting sounds like the best fit among these methods, in the next video I explain what really happens to the body during fasting, whether 16:8 is a magic number, and whether there are additional health benefits. See you there.

I hope this video helped you. You are also welcome to complete the short questionnaire below, which will help you think about which approach may suit you best.

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