Fitness, BMI & PKU

BMI is not a personalised reminder of your chocolate and/or beer binges. It lets you know roughly how you are doing.

Fitness, BMI & PKU

“Once you’ve filled in the form, we’ll get your weight, height & BMI.”

Ah the old chestnut, how does the BMI look today? Like many PKU folks, my body measurements are taken at every PKU clinic. I don’t weigh myself in between, but do get weighed on the odd GP visit. This means I have a fairly extensive record of my BMI going back (cough) 30+ years to childhood. While I try not to obsess about weight, I do look at these past measurements now and then. Oh, to be 18 again!

Last week, the GP’s receptionist told me it was weigh in time. I was quietly confident. It had been six months since my last encounter with the scales and I’ve been fairly active since then. The clothes are looser and I am completing my regular exercise class without resorting to easy setting so am definitely fitter and stronger. I was sure I weighed less. The only question was how much I had lost.

Nothing. The scales said my weight and BMI had gone up slightly. 300 grams gained, confidence lost.

Hold up! I know I’m fitter and stronger. They say that muscles weighs more than fat so… It’s an old saying but does that make it false? Another PKU patient, Kate Buckland, reported a similar experience in her piece for the Nutricia website:1 “Last year doing bodyweight High Intensity Interval Training I lost almost 3 dress sizes, 8% body fat and... 1.5kg. People kept commenting how much weight I'd lost, but I hadn't lost weight. I had lost fat and gained muscle, which is awesome!”

Beyond BMI

The NHS do confirm that “your BMI can tell you if you're carrying too much weight, but it cannot tell if you're carrying too much fat.”2 The same page tells us that “BMI cannot tell the difference between excess fat, muscle or bone.” Essentially BMI measures if you are carrying too much weight for your height, but it can’t tell you if that weight is excess fat or excess muscle. This is why athletes and gym bunnies are sometimes classed as obese under the BMI system even though they don’t have too much fat.

It is an important point to remember that BMI just gives an indication of healthy weight across a population. BMI is not a personalised reminder of your chocolate and/or beer binges. It lets you know roughly how you are doing. Another measurement that can help with that is the waist measurement. Again it only gives an indication, but an important one. If you carry too much fat around your stomach increases health risks. According to the NHS 3 I could do with losing a little more fat from my waist and shedding a few kgs overall.

Safe weight loss and PKU diets

It is widely agreed that losing weight quickly is not a great plan. The term ‘yoyo dieting’ is a commonly used when we work hard to lose weight only to see it all come back on again later. Slow and steady changes in habit and lifestyle are best. The NHS says we should be aiming for safe rate of weight loss ”between 0.5kg and 1kg. That's between around 1lb and 2lb a week.” 4

But before you work it out, remember that guideline is for normal people. Those of us with PKU are already on a restrictive diet, watching what we eat and obsessively counting intake is a daily necessity. Generally we are already eating pretty healthily and don’t have the quick gain of cutting out weekly visits to the kebab shop.

We also need remember that losing weight is a slow process, just as putting it on can be. My handy spreadsheet tells me that the last time I was in the healthy BMI range, Kate Winslet and Leonardo Di Caprio were running about on the Titanic. I plan to get back to that weight in less than 20 years though. That means I need to be more active. Damn it!

Getting started on getting fit.

Last year I had been toying with the idea of running more. This is unusual for me, I’ve claimed for years that “I only run for a bus or a train.” But as an inexpensive exercise that is easy to squeeze into a schedule, running is hard to beat. A pair of trainers and a bit of flat grass and away you go. I’ve found that heading to the local sports field means I can get in a warm up, a 30 minute jog and a shower done in less than an hour. (N.B. Different surfaces can affect your joints.5 I’ve found that running on grass works well for me and I don’t get knee pain. )

There are a lot of “Couch to 5K” apps out there, so I picked one up at the new year and gave it a try. Things went well until April, when holiday intervened and it was easier to just not pick it up again. I lost stamina, slept poorly and started feeling a bit blue again. But there was never the perfect day or time to get out there. It was too hot, too cold, too wet, too busy…Then, a friend said “when it comes to fitness, sometimes you’ve just got to do it” Turns out there is no magic button to make you fitter, just you.

So I laced on the trainers, walked out the door and got on with it. Yes, there have been times when I’ve cursed and maligned everything then walked home early. But there was also the joy of rainbow in a hail shower, the delight of being in just the right place to applaud wicket taking bowling and those wry smiles shared with the other regular joggers. Most important was that I would always finish with a sense of accomplishment.

Fitness and PKU

After a month or two of these runs, I was getting a few niggles and pains. As is so often the case, my first thought was “the diet is wrong again.” A quick email with the dieticians confirmed that the supplement I was on didn’t need adjusting. Along with Kate’s article, mentioned above, I found another guide on Nutricia’s website which helped with a few tweaks. Essentially, taking the supplements immediately after exercise had more benefit than taking them before. And when exercises last for less than an hour, we shouldn’t need to add any more meals and snacks to our diets. 6

This is true even for muscle building. I started doing yoga as part of my recovery from a brain injury (see here for more). Years of cycling and football meant I resembled a T-Rex. Good leg strength, puny arm muscles.

The planking, push ups and balancing exercises involved in Vinyasa flow yoga have improved my strength immensely. You don’t need to be taking protein packed power drinks to build muscle! It is as a relief to note that a few tweaks to when we eat and take supplements is enough to support a bit of strength building.

My last tip for this article is…

Have an exercise goal in the diary

I didn’t realise how motivating this could be until I tried it. There were plenty of goals that weren’t in the calendar: “I’m aiming for x -weight”, “when I get down to this dress size I’m off on a shopping trip”. There were also a few friends regularly checking in with how I was doing.

Despite these aims, I got stuck in a bit of a rut. Then a friend suggested aiming at an organised event. This would mean I had a date in the diary which I couldn’t push back or avoid. It sounded fun, then crazy, then daunting and finally all three.

In the end I went for it, and am now one of a team of 12 taking on a 5km obstacle course race in October. With that coming up, missing a run today seems like I’m robbing myself of a lot more fun tomorrow. It has added extra importance to the runs and helped to change round the exercises a bit. In preparation for the big day, a bunch of us are taking on a 30-day strengthening plan and texting each other with encouragement to take on the push ups.

Less than 30 days to go now so time to get out of the chair and raise the heart rate a little.

“This training just got real!”

(main image is from

  1. PKU & Fitness - The Challenge of Weight Loss, Nutricia Website September 2019. ↩︎
  2. Limitations of BMI section of BMI calculator page, NHS website. Accessed September 2019. ↩︎
  3. Why waist size also matters section of BMI calculator page, NHS website. Accessed September 2019. ↩︎
  4. Should you lose weight fast, NHS website. [] Accessed September 2019. ↩︎
  5. Top 10 surfaces for running on, Runners World UK website. Accessed September 2019. ↩︎
  6. Protein Needs for the Athlete on a Low Protein Diet, Nurticia website,-Senior-Metabolic-Dietitian/Accessed September 2019 ↩︎