Background
Methods
Study design
Participants
Participant | Sex | Main sport | Training volume (hours/week) | Age (yr) | Weight (kg) | Height (cm) | ∑8 Skinfolds (mm) |
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1 | Female | Cycling | 10–12 | 50 | 63.4 | 164.0 | 74.0 |
2 | Male | Running | 8–10 | 51 | 74.8 | 178.0 | 91.5 |
3 | Female | Running | 8–10 | 49 | 66.3 | 181.0 | 91.5 |
4 | Female | Cycling | 10–12 | 51 | 61.0 | 170.0 | 72.5 |
5 | Female | Cycling | 6–8 | 55 | 60.8 | 158.0 | 118.3 |
Study protocol
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Performance test. Participants reported to the lab in the morning in a fasted state and underwent a performance test on three occasions: i. one week prior to the intervention (familiarisation), ii. immediately prior to the intervention (baseline), and iii. Immediately post the intervention (post). To determine \( {\mathrm{V}}^{.}{\mathrm{O}}_{2\mathrm{peak}} \) and gas exchange thresholds (GET) an incremental cycle test was performed using an electromagnetically controlled cycle ergometer (Ergoselect 100, Ergoline, Bitz, Germany) in a temperature-controlled laboratory (21 °C, 65% rH). The test commenced at 30 W and increased by 30 W every 3 min until volitional exhaustion. Participants were instructed to maintain a cadence of 80 revolutions.min−1. Oxygen uptake (\( {\mathrm{V}}^{.}{\mathrm{O}}_2 \)) was measured continuously using a breath-by-breath metabolic system (Metamax 3b, Cortex, Leipzig, Germany), and heart rate was continuously measured using a short-range telemetry device (Suunto M2, Suunto, Vantaa, Finland). The \( {\mathrm{V}}^{.}{\mathrm{O}}_{2\mathrm{peak}} \) was defined as the highest 30s \( {\mathrm{V}}^{.}{\mathrm{O}}_2 \) value and the GET was identified independently by two experienced investigators using the V-slope method [11].
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Dietary instruction. An initial consultation was conducted with each participant by the primary researcher/Registered Dietitian directly after the performance test. Participants were provided with a daily macronutrient prescription of <50 g total carbohydrate, 1.5 g.kg protein and ad libitum fat. A detailed explanation of the practical application of the ketogenic dietary principles along with appropriate tracking and monitoring procedures was provided. Participants were provided with a sample diet and were advised to add variations as long as they adhered to the carbohydrate and protein macronutrient thresholds. They were instructed to track their diet using a dietary analysis programme Easy Diet Diary® (Xyris Software (Australia) Pty Ltd). Diets were monitored weekly by the primary researcher, and participants were contacted and offered additional support if they deviated. The primary researcher maintained regular contact with all participants throughout the 10-week study duration.
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Exercise instruction. The participants were all seasoned athletes, and participated on a regular basis in endurance events, i.e., mountain biking, road biking, running and multisport events (which included running, cycling and kayaking), both recreationally and competitively. Hence, their training protocols did not vary much from month-to-month. They were instructed to continue with their existing training volumes for the duration of the intervention.
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Ketone blood testing. Each participant was shown how to measure blood ketone levels via finger prick, and provided with a FreeStyle Optium ketone meter and ketone strips. They were instructed to measure their blood ketone levels daily between 2 pm and 4 pm. Nutritional ketosis was defined as a blood ketone (beta-hydroxybutyrate) level > 0.5 mmol/l.
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Anthropometric testing. Body weight and skinfolds were measured by an ISAK level one accredited anthropometrist, prior to and at the conclusion of the intervention, at the same time of the day. A sum of (∑) 8-site skinfold ISAK protocol was applied: triceps, biceps, subscapular, iliac crest, supraspinale, abdominal, front thigh and medial calf [12].
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Interviews and focus group. A 20–30 min individual interview was conducted on the phone during week 5 week and a 60-min focus group was conducted in person once the intervention had concluded. The importance of this qualitative work was to assess both the individual and the groups’ overall experiences of being on this diet for 10 weeks. The group session provided a chance for athletes to compare experiences and translate findings to future practice.
Data analysis
Results
Diet and ketosis
Participant 1 (male) | Breakfast ½ cup granolaa, 150 ml coconut cream, 100 g mixed frozen berries, 30 ml coconut oil | Lunch 125 g smoked salmon, 2 egg muffinsb, 100 g avocado | Dinner 120 g fish cooked in 1 Tc olive oil, 80 g broccoli, ½ cup almonds, 50 g feta cheese | Other 2 X Coffee (60 ml cream) Water |
Energy 2450Cal; Net carbohydrate 24 g; Protein 103 g (1.4 g/kg); Fat 215 g | ||||
Participant 2 (female) | Breakfast 3 rashers bacon, 2 eggs scrambled in 1 T coconut cream | Lunch Salad: spinach leaves, ¼ avocado, 30 g Gruyere cheese, 60 g salmon, spring onion, 1 T avocado oil, ½ cup sliced almonds | Dinner 100 g rump steak, salad (spinach, spring onion, pepper, carrot, desiccated coconut, 1 T pumpkin seeds), 2 tsp.d pesto | Other 40 g blue cheese; 180 ml red wine; herbal tea; water |
Energy 1710Cal; Net carbohydrate 9 g; Protein 94 g (1.5 g/kg); Fat 128 g | ||||
Participant 3 (female) | Breakfast ½ cup granola, 125 ml coconut cream, 50 g mixed frozen berries | Lunch 1 egg muffin, 100 g avocado, dessert spoon peanut butter, square chocolate | Dinner 100 g pork straps, 70 g spinach, 1 cup cauliflower rice, 1 T butter square 85% dark chocolate 180 ml red wine | Other Coffee, 100 ml soya milk; green tea; 1 strawberry; 20 g ham; 30 g almonds; water |
Energy 1768Cal; Net carbohydrate 33 g; Protein 76 g (1.1 g/kg); Fat 131 g | ||||
Participant 4 (female) | Breakfast ½ cup granolaa, 150 ml Greek yoghurt, 50 g mixed frozen berries | Lunch 95 g tin tuna, avocado, cheese, 1 T olive oil | Dinner 100 g chicken with skin, 1 tsp. soy sauce, 1 cup cauliflower, 25 g leek, 50 g asparagus, 1 T butter | Other 30 g salami; ½ cup almonds; coffee, 150 ml milk; 100 ml coconut cream, water |
Energy 1919Cal; Net carbohydrate 31 g; Protein 96 g (1.5 g/kg); Fat 154 g | ||||
Participant 5 (female) | Breakfast 2-egg omelette (spinach, mushroom) cooked in 2 tsp. butter | Lunch Salad: 1 cup mesclun leaves, ½ avocado. 30 g feta cheese, 90 g chicken, 6 baby tomatoes, 50 g cucumber, 30 g celery, 2 T olive oil | Dinner 120 g fish, stir-fry vegetables (1 medium zuchini, 50 g broccoli, 5 mushrooms, ½ brown onion), cooked in 1 T olive oil | Snacks 100 ml coconut cream; 30 g almonds; water |
Energy 1406Cal; Net carbohydrate 19 g; Protein 93 g (1.5 g/kg); Fat 103 g |
Substrate oxidation
Body composition/performance
Athlete experiences
Positive themes | Negative themes |
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Physical recovery
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Loss of power during exercise/training
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“The recovery each time was amazing. I would go for a 4–5 h run then be able to mountain bike the next day, just to be able to do it without sore muscles”. “The next day after a 4-h run I could have got up and done it again - my legs weren’t tired or sore”. “Certainly I’ve had the recovery benefits I felt fine to go out the next day and do stuff I didn’t feel the muscle soreness I would have expected”. “I don’t feel sore”. “I was surprised that I could run comfortably for that long so I think the recovery was huge I never felt this, it’s unheard of” | “It was embarrassing to the point where I just got to the point where you just don’t have any energy”. (weeks 1–5) “I got too tired and I got to the point where I might have had some big runs, 4 or 5 h runs and wake in the night before hand, worried about it. I’d think, how am I going to do that tomorrow… it’s going to be hard”. (weeks 1–5) “The lack of power, I just couldn’t get up the hill.” (weeks 6–10) |
Negative symptoms (weeks 1–3)
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“I hadn’t been for 4 days and I was starting to get bound up”. (constipation). “One of the downsides is that I had cramps, massive cramps”. “I may have seemed a bit irritable for a while. People close to me realised I was down and I’m pretty good at hiding that but people picked it up”. | |
Enjoyment of this way of eating
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“It’s given me the freedom to eat the things that I stopped eating for a long time because I thought it was a no-no”. “Not feeling hungry has been amazing”. (X2) “Not being bothered about food, you know food doesn’t bother me anymore, as before I had a meal and 3 h later I’d feel irritable if I didn’t eat”. “It’s been fantastic for me having food I couldn’t for a long time and I really enjoy it, the flavour, for me the reason why I want to carry on with this way of eating is because I actually enjoy it, I enjoy it far more than my previous diet”. | |
Food regime boredom
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“Bored with the food regime, actually I’m back on fruit …” “…but I am starting to get sick of the diet plan”. “You can’t even free load in your veggies.” | |
Weight management
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“Being able to shed that 5 kg was definitely a benefit”. “The benefit now of me being able to understanding how to manage my weight, that’s been a real effect, actually that’s been for all of us”. | |
Feel better overall (well-being)
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“My skin hasn’t been this good since I can remember”. “My prostate, a million times better because I can sleep”. “The other thing I noticed is my tinnitus is a lot better, I can’t hear the ringing in my ears I used to have”. “Just general health - I just feel better, I need less sleep”. “I noticed that I didn’t fart for 2 months, no gas”. “Yes, no gas, that’s the same as me.” “I feel sharper mentally”. “Food used to dictate my moods, and now it doesn’t”. “Positive skin, I have a facial every 6 weeks, I didn’t tell the facial lady what I was doing and she said to me what’s happened to your skin? No extractions in the last 8 weeks, no blockages”. |