All You Need to Know About Dieting From a Doctor Now

Maybe you are feeling a bit unhealthy, or have gained some weight, or are considering getting back in shape. Are you trying to choose a diet, but you don’t know where to start? How do you sort the sometimes risky fads, from a sustainable and healthy way to get to your target weight? I’ll talk through the most popular diets, and give you tips on eating for health and weight long-term. Does intermittent fasting help with weight loss? Read on to find out all you need to know registered nutritionist and doctor about diets.

How to choose a diet?

There are so many diets, how do you choose one? Maybe you follow a celebrity, or the diet your friends are doing but have you considered what the evidence is behind many diets? Do they really work, are there any potential risks? How do you find one that improves your health, not just your weight?

How does a doctor choose a diet?

Balancing Macronutrients

Food is comprised of water, macronutrients and micronutrients. Macronutrients can be split into 3 groups, protein, fat, and carbohydrates, while micronutrients are vitamins and minerals.

Only macronutrients contain energy or calories. Protein and carbohydrates have 4 calories per gram, while fat has 9. Alcohols are also found in food, and have calorific value, but are not usually included as a macronutrient because they are not required to survive.

eat for health

You might have heard people talking about “balancing their macros”. This just means working out the balance of macronutrients (fat, carbohydrates and protein) on their plate. This is often done with the goal of weight loss.

It is similar to calorie counting, in that mostly people set themselves an allowance of protein, fats and carbohydrates, in the same way you might set a calorie target.

Then you can choose to how to eat your macro allowance. For example, say you decide to eat 100g of protein an 50g of carbohydrate, you could eat a piece of grilled salmon with sweet potato, or deep fried chicken wings.

Just because you are counting macros, does not mean that you will make healthy choices. However, one of the positive differences between counting macros versus calories, is that counting macros is more likely to help you have a balanced diet. Since with calorie counting, your calorie intake could just be made up from only carbohydrates, whereas with a macro allowance, you are guided to eat from all 3 groups. The down side of macro counting, is that like calorie counting, it can be restrictive, and difficult to maintain, as you have to calculate the quantities of all your food.

Calorie Counting

A calorie (cal): is the energy required to raise the temperature of 1g water from 14.5 to 15.5°Celsius. This is calculated in a laboratory, by burning the food. However, the food is not ‘burnt’ in our bodies, and people’s metabolism and energy expenditure vary, so it’s a very rough estimate.

In addition, how the food is processed, also affects the absorption, and therefore how much energy is available for you to use. A good example of this is sweetcorn. If you grind it down into a powder and make a tortilla, you will absorb far more calories than if you eat whole sweetcorn kernels, as you will see most of them untouched, in the toilet!


Another concern with calories, is that instead of thinking about nutrient quality, it promotes prioritising quantity. For example, there is a huge difference in the number of nutrients you could consume in 500 calories of ice cream, versus 500 calories of fruit and vegetables.

Also the number of calories you need varies according to so many factors, such as age, sex, lifestyle, activity level, that it is hard to accurately predict exactly how many you need.

As a registered nutritionist and doctor, I wouldn’t chose to restrict my diet with calorie counting.

Blood Group Diet

First up is the blood group diet, popular with celebrities all over the world (Cheryl Cole, Liz Hurley, Courteney Cox). Each red blood cell in our body is labelled with markers that are called the ABO blood group system. ⁠Using two markers, ‘A and B’ there are 4 different combinations: O no markers; only A markers; only B markers; and A and B combined to form AB. ⁠

all you need to know about dieting from a doctor and registered nutritionist

The premise of the diet, is that different blood groups, need to have a different diet. However, there is no evidence that diet and ABO blood group type are linked. ⁠

Instead, any benefit is probably due to increased mindfulness of eating, and an element of dietary restriction. ⁠After all, junk food is off limits on the ABO diet, which means that you would be eating more healthy food, but without any relevance to your blood group. ⁠

Low Carbohydrate / Ketogenic Diets

Low-carb diets involve consuming less than 26% of daily energy from carbohydrates, compared to government healthy eating guidelines which advise about 50% of daily energy from carbohydrates. There are lots of slightly different low-carb diets in the media such as the ‘keto’ and ‘Atkins’ diets, which have gained popularity due to short-term weight loss. 

Ketosis is a metabolic state which occurs to those following a very low-carb diet plan (i.e. including only 5-10% of energy from carbohydrates). Instead of breaking down or ‘burning’ carbohydrates (the body’s preferred energy source), cells are forced to break down fat instead.

When this occurs, specific chemicals, called ketone bodies or ketones are formed, and this is why it is called ketosis or ketogenesis. So this type of low carbohydrate diet mimics the fasting state.

The ketogenic diet (or the keto diet for short) was developed for children with treatment-resistant epilepsy, as a short term measure to get their seizures under control.

The diet was designed to be used for a maximum of 2 years and to be stopped early if seizure control was not achieved. However, this diet has become popular in recent years with the aim of promoting weight loss. 

eating for health

Pros of Low-Carb Diets:

There is evidence that short-term use of these diets may lead to weight loss, but no evidence of superior weight loss in the long term. Better short term control of blood sugar in type 2 diabetes has been associated with a low-carb diet, but again there is insufficient evidence of long term benefit.

Low-carb diets which are high in plant-based protein and plant-based fats have been shown to be associated with decreased mortality and cardiovascular risk.

doctor diet

Cons of Low-Carb Diets:

Some people get the ‘keto flu’ when they follow a very low-carbohydrate diet, with symptoms such as diarrhoea, tiredness, cramps and headaches.  The brain preferentially uses sugars from healthy carbohydrates, lack of these can lead to confusion and irritability.

Eating a limited range of food (especially fruit, vegetables and wholegrains) can lead to micronutrient deficiencies. While fruit and vegetables contain natural sugars, they also contain fibre, vitamins, minerals and antioxidants in the form of polyphenols. 

So a low-carb diet can lead to a lower fibre intake which can increase the risk of constipation, negatively impact the microorganisms which live in the gut and contribute to an increased risk of bowel cancer.

Low-carb diets can often become high in saturated fat, which can lead to an increase in Low-Density Lipoprotein (LDL), known commonly as the bad cholesterol. This can increase the risk of fatty liver and cardiovascular disease.

all you need to know about dieting from a doctor and registered nutritionist now

A restrictive diet is difficult to maintain, and therefore any weight loss is likely to be temporary. Furthermore, a lot of the initial weight loss due to reducing carbohydrate intake tends to be water weight.

Data from a large meta-analysis (grouped analysis of a number of studies) and long term prospective study which followed people for over 20 years, found that a low-carb diet, where less than 40% of daily energy was coming from carbohydrate, was associated with a higher risk of early death.

However, within this data set, there were two very different groups. For those people who substituted carbohydrates with plant-based fat and protein, they had lower mortality and cardiovascular risk.

While those people who substituted carbohydrate with animal-based fat and protein had a higher risk of mortality and cardiovascular risk. This restriction also risks creating an unhealthy and obsessive relationship with food.

Read more about low carbohydrate diets here. I hope you have found this article, all you need to know about dieting from a doctor now helpful so far. Next I’m going to discuss the evidence behind fasting.

Intermittent Fasting and Time Restricted Eating

There have been many studies now providing a large body of evidence about what happens when we intermittently fast. Some of this research has been performed in animals and then replicated in clinical trials on humans. While intermittent fasting is associated with weight loss, there are also profound metabolic changes that happen too, that are thought to be separate.

doctor diet intermittent fasting weight loss

Metabolic Changes

Intermittent fasting elicits evolutionarily conserved, adaptive cellular responses that are integrated across the body. This fasting induces cells to switch on a coordinated response to stress, with resultant increased expression of antioxidant defences, repair of DNA, higher standards of protein quality control, and reduced levels of inflammation.

Animal Studies

A number of studies have now compared body composition and weight in mice on either non-time restricted diets or time restricted ones.

Below is an example of one such study, that compared a high fat diet and normal chow diet in mice (Hatori et al., 2012). The mice were randomised to receive either diet, and then further randomised to eat either whenever they fancied, or only within an 8 hour window each day (Hatori et al., 2012).

Regardless of the time the mice were allowed to eat, the total calorific intake was the same depending on which diet they were on. The image below shows two example mice, both who were on the high fat diet.

One could eat whenever they fancied (FA), while the other had the same diet, just ate it all within 8 hours per day (FT). This study demonstrated that time restricted eating (intermittent fasting) can protect against the weight gain usually seen with eating a high fat diet in mice (Hatori et al., 2012). These protective effects were also seen at a metabolic level as well.

intermittent fasting weight loss and doctor diet

During fasting there is good quality evidence that the following things happen:

  • cells activate pathways that enhance defence against stress (metabolic and oxidative) including increased antioxidant defences, DNA repair, and protein quality control.
  • damaged molecules are preferentially removed or repaired.
  • cellular responses lead to improved glucose regulation, increased stress resistance, and suppression of inflammation.
  • formation of chemicals called ketone bodies, (or ketones), which may have positive effects on brain health, and in particular working memory.
  • while some of the health benefits are due to metabolic changes, some are because of the associated weight loss.
  • but even in non-obese people enrolled in a multi-centre trial, daily caloric restriction still improved cardio-metabolic risk.
  • these pathways are only activated by fasting, and are suppressed or unused in people who are sedentary and overeat.
  • 2 studies showed that 24 hour fasting 3 times a week reversed insulin resistance in patients with pre-diabetes or type 2 diabetes.
  • intermittent fasting in humans and animal studies improves blood pressure, resting heart rate, cholesterol profile, glucose and insulin levels.
  • many animal studies have shown daily or alternate day caloric restriction reduces the occurrence of spontaneous tumours in rodents, while increasing sensitivity to chemotherapy and irradiation.
  • preoperative fasting reduces tissue damage and inflammation and improves the outcome of surgical procedures.


Even if you are not looking to lose weight, intermittent fasting has the potential to have wide ranging positive effects on your health. Many people say the major hurdle to changing the timing of eating, is going out to work, so with more opportunity for working from home, it might be a great time to try. As a doctor, this diet provides a substantial body of evidence of wider benefits for long term health and is worth considering.

For much more information on intermittent fasting, including how to start, side effects, and cautions, see here.

Summary: All You Need to Know About Dieting From a Doctor Now

all you need to know about dieting from a doctor and registered nutritionist now

I hope you have found this article about all your need to know about dieting from a doctor and registered nutritionist helpful. I’ve talked through the evidence about different diets, and intermittent fasting associated with weight loss. Instead of following a restrictive set of rules, that are hard to follow long term, and have the potential to create unhealthy relationship with food, try my tips instead.

Practical tips for eating for health long term:

  • Don’t impose a set of strict restrictions on your diet, but make healthy choices at every available opportunity. 
  • Eat a variety of food, that will ensure you get the micronutrients you need and help your gut health. 
  • Aim to fill your plate with about 50% colourful vegetables and fruit, 25% lean protein, and then 25% healthy unsaturated fats and whole grains. 
  • Eat mindfully only when you are physically hungry and stop when you are full. Read more information here.
  • Consider supplementing your diet with vitamin D, omega 3 and if you are vegan B12. 
  • Avoid processed meat that is preserved by smoking, salting or with chemicals such as nitrites. 
  • To reduce cost and increase availability out of season try more frozen and freeze dried fruit. 
  • Ensure you are eating 30g of fibre per day and a variety of legumes, beans and pulses. 
  • Add a handful of nuts to your diet per day. 
  • Use extra virgin olive oil for cooking as well as garnishes.
  • Consider intermittent fasting or time restricted eating but discuss this with a registered nutritionist first.  
  • Check you aren’t thirsty instead of hungry by having a drink of water. Read more about how much you should drink here.
  • Enjoy food!

These will enable you to eat for health, and decrease your long term risk of disease.

eating for health and intermittent fasting weight loss

Looking to understand how to create a personalised healthy meal plan? Check out this article. For more evidence based nutrition information see my self-paced online video courses to guide you to eat for long-term health.

If you enjoyed this article you might find intermittent fasting, metabolism, stress and nutrition, how much water should you drink and emotional eating useful too.

I’ve also got a range of free nutrition planners and checklists depending on your stage of life, choose from adult, fertility, pregnancy, breastfeeding, menopause, PCOS and vegan.

2 Replies to “All You Need to Know About Dieting From a Doctor Now”

  1. Thank you for providing so much information about the pros and cons of the various approaches to dieting. Really appreciate your knowledge and generosity.
    Aa a life long dieter, and having lost the same 2 stone at least 5 times over the last 7 years, I am weary and confused about the best approach, but your site is very helpful.
    Thank you, Ellen

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