Successful Weight Loss: Which Diets Work?

By a Lifestyle Medicine Physician

Whether it is thinking back to Christmas indulgences, or looking forward to warm summer days spent on the beach, there often comes a time when getting into shape comes to the forefront of peoples’ minds.

There is quite a lot of scientific data on weight loss methods. Ultimately they mostly come down to three different mechanisms.

I will explain each in turn.

Just so you know, they all work — sort of.

But there are caveats.

I will go through these caveats in my next post ‘How to Lose Weight..Part 2: Caveats of the Weight loss Diets’

Overview of the main weight loss types

Weight Loss Method 1: Calorie Restriction

This is the type of weight loss method used by the likes of Weight Watchers® or Slimming World®. In truth, even diets like juicing are really aiming to keep the calorie count down by restricting what is eaten, although in this case it also seeks to maximise nutrient availability (see my article ‘can I drink my 5 a day’ to see how juicing may not lead to weight loss however).

Fundamentally, if you take in fewer calories than you use, then you should lose weight. By becoming aware of the calorie count of various foods and making sure that you stick to your calorie quota, over time it should mean that you lose weight.

It works.

Weight Loss Method 2: Low Carb Diets

Low Carb (Carbohydrate) Diets like the Atkins Diet® or ‘ketogenic’ diets aim to minimise carbohydrate from the diet. Instead, the diet ramps up the other two macronutrients: protein and fat.

These diets use the clever physiological trick that if you don’t supply carbohydrate to the body it won’t produce insulin. If it doesn’t produce insulin it won’t store fat. Your body switches to using fat as a fuel by a process called ‘ketosis’. This is necessary because whilst your body can burn all three macronutrients (carbohydrate, protein and fat) for fuel, your brain can ONLY use glucose (carbohydrate) or ketone bodies (formed by burning fat via ‘ketosis’).

Ketogenic diets have been used therapeutically for patients with epilepsy. They were originally developed because fasting had been shown to reduce epileptic seizures within 2–3 days. But starving epileptic patients for days didn’t seem a very practical method. Thus the metabolic trickery of the ketogenic diet was born.

Since then there is evidence that ketogenic diets may hold therapeutic potential for a variety of brain disorders such as multiple sclerosis and Alzheimer’s disease.

Low carb diets have also been popularised for reversing diabetes. In the same way fasting improves brain excitability in epilepsy, it improves insulin sensitivity in diabetes. So the metabolic trickery works here again.

But low carb diets have gained great popularity in particular for weight loss.

If we take the Atkins diet, we can see how it is proposed that you enter — and sustain — a ketogenic state. It has 4 phases.

Phase 1 lasts roughly 2 months, and it restricts nearly all plant foods because they have a high carbohydrate content compared with animal foods. You are allowed a 12–15g portion of cooked veg or salad however (normal dietary guidelines suggest 400g/day of fruit and veg so you have a sense of context). Phase 1 is really the big hitter with weight loss, but it would be very difficult to live like this long term. Enter phases 2–4. These allow you to gradually increase carbohydrates starting with those with the lowest glycaemic load. Ultimately, long term you will always aim to keep to a low carbohydrate intake.

And they do work.

The Paleo diet

I give special mention to the Paleo (Paleolithic) diet here because although it isn’t intended to be low carb, in practice it often is.

The Paleo diets try to duplicate what may have been eaten in the Paleolithic era: 10 000 to 2.5million years ago -so:

-no processed foods, no dairy, no cereals, no legumes,

-plenty of wild fish and grass fed meat, vegetables, fruit, nuts and seeds

In the Paleo diet the quality of the food is paramount.

In ketogenic diets such as Atkins, the quality is not really important, it is the macronutrient (carbohydrate/protein/fat) content that matters.

Again, studies have shown that the Paleo diet is effective for weight loss.

Weight Loss Method 3: Whole Food Plant Based Diets (WFPBD)

These include Vegetarian, Vegan and Mediterranean dietary patterns. Each of these diets are plant predominant — so they are really focussed on maximising the intake of nutrient-rich components of the diet. They each have a variable amount of animal products, with the vegan diet having none.

Some of these diets have cultural or religious origins. A lot of rural cultures would find animal products to be too expensive, so whilst not calling themselves vegan would have lived in this way.

Vegetarianism similarly is common in certain cultures, especially in India.

The Mediterranean diet when talked about in the Scientific literature refers specifically to a diet based on what would have been eaten by rural inhabitants of the Mediterranean basin in the 1960s rather than what is typically consumed today.

As such, these are typically not designed for weight loss, but very large studies have consistently shown that the more plant based the diet, the slimmer people are.

For example, the ongoing European Prospective Investigation into Cancer (EPIC) Oxford study has found that -despite having a particularly health conscious sample — amongst the nearly 38 000 people they have followed up, there is a stepwise fall in BMI with fall in animal food consumption, and as people move towards a plant based diet they gain less weight.

The fact that plants are very low in calories and high in fibre means that people who eat like this get full on very few calories so they tend to be slim — as long as they consume whole foods rather than processed foods.

As this paper from the World Health Organisation notes, when people are advised to increase fruit and veg in their diet and reduce fat, they spontaneously lose weight — even when there is no emphasis on reducing weight. This is because fruit and veg are so low in calories, and they increase satiety which is a feeling of being full. They also suggest that the message of eating plenty versus restricting food is much easier to stick to.

So, plant-based diets work.

A comparison of the main diets have found that there is no significant difference between the amount of weight lost between each one.

So, what are the caveats?

Read my follow-on article ‘Successful Weight Loss — Part 2: Caveats of the Weight loss Diets’ to find out which some surprising differences between what you lose on each diet.