When clients start a Low-Carb eating plan, they frequently worry that they will not have enough energy to get about their daily tasks or to exercise. 

In the first 3 weeks of the Low-Carb plan I discourage intensive exercise, as you will need time for the body to adapt to burning fat.  In recent weeks I have a few clients who are climbing and cycling so I did some research. 

Where does energy come from?

The body is capable of producing energy from carbohydrates (carbs), fats, proteins and alcohol. Alcohol cannot be broken down by the muscles, it has to be broken down by the liver making it a slow source of energy and a load on the liver.

Which foods deliver the most energy?

When you look at food in terms of calories, it seems obvious but the body is complicated!

1g fat = 9 calories and calories are energy, ATP

1g Alcohol = 7 calories

1g carb = 4 calories

1g protein = 4 calories

Which energy does the body use?

For sudden bursts (a heavy weight-lift or a sudden sprint) the body uses a protein called creatine, (PhosphoCreatine) but it is used up really quickly and its supply is limited.

By warming up you are increasing blood flow, rich in oxygen and nutrients, to cells all over your body which improves energy production. Without oxygen, energy production is low; ATP is a unit of energy

Without Oxygen 1 glucose molecule produces 2 ATP

With Oxygen      1 glucose molecule produces 38+ ATP

With Oxygen      1 fatty acid              produces  80 to 200 ATP

TIP: Always warm up and always get blood with oxygen circulating so that you get maximum energy flowing. Get on the threadmill or bike before you lift weights. If you are climbing a steep mountain, walk on the flat for 15 to 20 mins before you start climbing.

Note above, how fat produces more energy than carb once your body adapts to burning fat. Fat cells store massive amounts of energy.  

The body stores little carbohydrate, only 520g of carbs as glycogen. Muscles store about 400g of glycogen (glucose attached to water 1: 3) and the liver stores about 100g of glycogen.

TIP: If you build up your muscles, you will store more glycogen.

The body stores no protein.

What do I do if I am heading out on a long cycle or hill walk?

It depends on:


If you are aerobically fit, your muscles have adapted and will be able to break down fat very quickly regardless of the exercise intensity. This is such a great motivator to get fit as it will help you maintain your weight. A low carb eating plan should, in theory, suit you really well if you are very aerobically fit, with little need to fill your muscle stores with carb beforehand. However, I would take 100ml of orange juice in water to make life easier for the muscles and support recovery. Enter it in your APP and overtime you are the best person to assess if you need more as you time your exercise and recovery.

If you are not aerobically fit, you are unlikely to work out at an intense rate and will burn fat as you pace yourself.


How breathless do you get and for long are you breathless? A flat cycle and a friendly walk are low intensity and the body happily uses fat as the fuel. If it is a nice mix of short hills mixed with flats and downhills, again you will be fine on a low carb food plan.

If the cycle is intense (hilly) or you are really pushing it, climbing a steep hill for 1 to 2 hours and feeling so breathless that conversation is difficult, you will need some carbohydrate. For this type of long and intense session I suggest taking a water bottle with 400ml of orange juice (32g carb) that will enter your bloodstream quickly. Drip feed it into your blood stream before the hilly section hits so that muscles can suck it in and fuel themselves.


If the intense exercise lasts > 3 hours or is a day event, start refuelling your muscle stores the night before and at breakfast. It can take up to 20 hours to refill muscle glycogen stores if you have been on a keto plan or low carb plan.  

Athletes are advised to eat 4g to 5g of carb per kg Bodyweight per day to support their training.

We are not athletes and athletes are at their ideal body weight. My clients are not at their ideal bodyweight.

For my clients whose main goal is to achieve a healthy lean bodyweight and get fitter, I suggest eating 1g-2g of carb per IDEAL kg bodyweight on long days of intense exercise. Otherwise a little juice in water should be enough to support the muscles in strength training and short aerobic activity.

For Example

Female ideal body weight 68kg x 1g carb to support intense exercise < 2 hours = 68g carb  

Female ideal body weight 68g x 2g carb to support an intense day of exercise > 3 hours = 136g carb.
The same applies to Males e.g., 85kg x 1carb or 2g depending on duration & intensity = 85g to 170g carb

Eat healthy carbs such as 60g oats with 250ml milk and 80g berries (totalling 54g carb) upon rising. If you are starting out early, eat the night before, a low GI pasta (raw 60g = 33g carb) and meat dish with veggies, topping up with breakfast or juice on the hike or cycle.

Most of my clients do not undertake high intensity exercise and a lot of my reading is based on studies done on athletes however it is good to know when to fuel with carbs.

TIP: Fuel the night before with low GI carbs, if you are starting our early on a long, intense cycle/hike so that muscles have an immediate supply.

What do I do if I am going to the gym for a strength session with little to no aerobic activity involved?

Weight training relies on carbs stored in muscles or glucose in the blood steam. A strong, intensive muscle training session will deplete carb stores and the body will burn the muscle protein that you are breaking down. It is ok to burn protein as a fuel in weight-training because the purpose of weight-training is to break down muscles so that they build back stronger. However, ensure you replace the protein with a whey shake during or within 30 minutes of completing your session. Add a little orange juice to the shake to support the exercise and muscle recovery. 

What is your favourite benefit from exercise?

You have a 30-minute window after exercise when the glycogen stores get refuelled really quickly as the muscles suck in glucose from the bloodsteam. Use this window to eat the carb you really love, guilt-free but log it in your APP.

Is it good to sweat?

The body produces heat and energy from food. For example, when cycling, only 20% of the energy is converted to power, the rest becomes heat. The body sweats to cool itself down. It is great to sweat. It is essential to put water back in or you will stress the entire body.

In Summary

  • You have lots of energy on your body in the form of fat and your body can and will burn it.
  • As you get more aerobically fit, you will need less carb and become better at fuelling on fat for low intensity exercise.
  • If you are doing an intense form of aerobic exercise that makes you very breathless and lasts longer than 2 hours, take on 1g – 2g of carb per your ideal bodyweight in kg to support your muscles and reduce muscle soreness.
  • Eat the night before if you are starting out early on a day’s hike or cycle. 
  • For an intense gym class which involves sprints and weights and lasts just 45 mins including warm-up and cool-down, and you feel you need more energy, take a fast sugar like orange juice (150ml = 12g carb) in a water, sipping it to put glucose into your blood for your muscles before, during and after the class. 
  • Always warm up and get the blood flowing around to all cells before you rev up the intensity

Note: Reference Guide: Sports Nutrition. Anita Bean.

These guidelines are for my clients only who are in daily contact and guidelines can be adjusted based on results reported to me.

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