Whereas at the time the notable RD’s tome was timely and cutting edge, the preceding couple of decades have rendered much of the book’s conventional wisdom somewhat outdated and possibly to some extent currently off-base.
To preface, it’s worth noting that Kleiner has since released a sequel to the book, The New Power Eating, that is certainly more up to date on today’s knowledge. But still, I’m curious to see how well the old edition holds up.
Kleiner obviously didn’t err based on the information available to everyone in her field at the time. No one then knew of the benefits of concepts like intermittent fasting, carb cycling, that the kidneys could in fact handle a large amount of protein without ill effect, that we didn’t necessarily need as much carbohydrate as they thought for intense activity, etc.
I’m reading through some of the book now, primarily initial sections on exercise fueling, before and after training. She echoes a lot of the conventional wisdom regarding endurance running nutrition, which as people know is very high-carbohydrate and carb-centered.
While the following is hardly comprehensive, I have read a few interesting points that are either not necessarily true today, or could well be valid today and has not been carried over into subsequent analyses.
Kleiner recommends a diet of 20% protein, 2.2g/kg max for high performance athletes
There’s a bit of cognitive dissonance with these recommendations, as unless you’re eating a very large number of calories, a diet of 2.2 grams protein per kilogram of body weight would require a lot of total calories for that to represent only 20% of your calories. By high performance athletes, I mean Kleiner is discussing athlete who strength train AND aerobically train on a very regular basis (5+ days per week of both).
For example, I’m currently around 77 kg. That indicates I would need 169g of daily protein. That makes relative sense against the recommendations of other fitness writers focused on strength training.
(Obviously, writers who focus on running would say I need a lot less, but there are various issues regarding the conventional nutrition wisdom of those writers that I won’t get into right now.)
For 169g of protein to compose 20% of my daily diet, I would need to consume 3380 calories. That is quite a bit, even considering I burned and consumed around 3000 or so calories a day in Chicago while high-volume training as a runner, when I maintained a consistently lower weight around 160-165 lbs. I certainly approached those daily dietary numbers but never consistently ate 165-170g of protein nor 3300-3400 calories a day. In both cases I averaged somewhat less, though it was more like 140-150g and 3000-3200 calories.
Still, that’s quite a bit, and approaching that mix of numbers worked for me because I ran 35-50 miles a week plus walked dozens of additional miles having to walk everywhere to get around in Chicago. Once my general activity decreased around late 2018, that was way too much and my weight began to steadily climb.
Consume 50g high glycemic carbs ASAP following intense exercise, 100g+ within 4 hours
This is in line with conventional runner’s wisdom that you consume carbs and protein within 30 minutes to 2 hours, to restore glycogen and take advantage of increased absorption.
However, running writers’ advice can vary on how much to consume, whereas Kleiner puts a hard number on the recommendation. And it’s worth noting she handles nutrition for not just competitive runners but all kinds of competitive athletes across all sports. The recommendation is universal.
Now, I like to offer the caveat that the less competitive your training and goals are, the less often you train, the less important it is for you to consume within those windows. However, most runners have fairly specific goals, and that’s suitably competitive for a recommendation like this to remain important.
The big clash with this advice is the same as the big clash broscientists, paleos and lifters have with most running minds: The need for regular carbohydrates and whether or not it’s more valuable to train the body to be fat-adapted. The rising Primal/Paleo school of thought is that it may benefit you to decrease overall carb consumption and develop within your body the tendency to draw more upon fat for aerobic demands.
I can certainly see a debate from both sides on the subject, the long term health ramifications of high carb consumption vs the body’s inherent ability to maximize performance using glycogen along with the inherent slowness of fat usage in intense exercise.
I also have thoughts on that idea that I can share later. But for now, it’s clear that Kleiner was probably ahead of her time in terms of defining carb intake for athletes before and after training to properly fuel performance and re-fuel for future activities.
600g max carbs per day, due to body’s glycogen storage limits
Kleiner is fairly clear about how the body can only restore its glycogen stores with up to 500g of consumed carbs in a day, that beyond 500-600g the body cannot store or utilize any more consumed carbs for glycogen.
You will often see running writers recommend large amounts of carb consumption, up to 8-10g per kilogram, which can translate to up to 800g of carbs ingested per day. Kleiner points out that there’s a threshold at no more than 600g where the body simply cannot use any more consumed carbs, and that any consumed beyond that is basically wasted.
Now, there could be a caveat I missed with carbs consumed before or during exercise. Kleiner points out to try and hit this 600g threshold during the 24 hour window after exercise. The period before and during exercise could be fair game, of particular importance to marathoners or other long distance runners, who will certainly burn a lot of glycogen during training and likely will consume some carbohydrate during training. Should that be included with the 600g consumed after training? Could it be okay to consume more than 600 in a day as long as you take in a bunch of fast-burning carbs during training?
Insulin in blood is an anabolic hormone
This points to a common misstep by broscience and paleo lifters. Their typical vilification of carbs overlooks the importance of the insulin that carbs help create. Kleiner helpfully points out that insulin is an anabolic hormone, and thus very important to muscular development.
Because of its relationship to diabetes, a lot of paleo and carnivore bros will argue against carbs by pointing out the insulin resistance creating effects of the body overproducing insulin. Thus insulin production from carbs is bad and we should avoid it.
Of course, they overlook that exercise increases the receptivity of insulin in muscles, and thus by training you are actually using all the insulin that’s being produced by those carbs. And your muscles certainly have a use for that insulin they’re taking in!
This is not to say go eat a bunch of processed garbage. Processed garbage has a lot of terrible side effects that can undo the benefit of whatever insulin those refined carbs may produce. You still want to get your carbs from clean, whole food sources.
But carbs are no more of a demon than it is essential that you eat hundreds of grams of them a day. The modern day truth is somewhere in the middle of Kleiner’s 600g a day recommendation and the broscientists’ recommendation that you avoid non-fibrous carbs at all costs.
Oxygen must be present to burn fat, and suitable oxygen takes time to get to muscles
Running minds always point out how slow fat is to burn, and unlike them Kleiner to her credit explains in detail why fat is slow to burn.
While personal trainer texts will spell out how fat generates energy via oxidation, Kleiner in this book actually connects the dots between that biology and why fat burns so much more slowly during exercise.
Fat requires oxygen to be utilized as fuel, and when you begin exercise your stasis-level of oxygen is not enough to effectively port that fuel to your muscles. You have to slowly, gradually increase your oxygen intake for fat to effectively get involved, and this according to Kleiner can take up to 20-40 minutes no matter how intense your effort.
Now, this points to a possible reason the Wim Hof Breathing Technique is so effective for athletes who use it. By pre-empting exercise with a series of coordinated breaths (or lack thereof) to hyper-oxygenate your blood, you more quickly engage that available fat for energy.
This actually points to why many personal trainers have trainees start training with a longer, intensity-ramping aerobic warmup. By quickly and briefly approaching the lactate threshold, you accelerate the body’s oxygen intake and availability, which is where the trainers’ advertised “increased fat burning” comes from. You have more oxygen earlier in training, and can tap into fat to burn more quickly.
Wim Hof’s method effectively skips ahead to the increased fat burning without 10 increasingly brutal minutes on a treadmill or spin bike. The only thing brutal about the breathing technique is breathing harder than you’d like, and having to hold your breath for as long as you can handle a couple times.
Now, Kleiner at the time didn’t know Wim Hof from Adam, because Hof didn’t become popular for his method until long after Kleiner first published Power Eating.
But Kleiner’s findings do speak to the possibility that Primal Endurance‘s mythical “fat adaption” in endurance exercise could be more easily acheived if you warmed up with the Wim Hof Breathing Technique.
If by the time you take your first rep or running step you already have from Wim Hof Breathing a higher oxygen level present in your blood, you can more immediately and efficiently tap into your fat stores for energy. This at the very least decreases the overall glycogen you will need.
This idea is worth exploring further.
Now, does Kleiner’s Power Eating hold up? Sure, some of this material is outdated and has since been disproven by subsequent discoveries. And I’m sure Kleiner herself would admit that, if The New Power Eating hasn’t updated her principles and advice on those topics.
Still, a lot of the original’s material not only would help traditional endurance runners… if they’re going to insist on a high-carb diet and lifestyle, they probably should grab a copy of this book and read it. Kleiner does explain and illustrate a lot of conventional runner wisdom, showing the science behind where those beliefs came from. And it gives a firmer, clearer baseline to some of that conventional wisdom.
As I said before, people can debate the benefits of high vs low carb consumption in athletic training, whether it’s possible let alone practical. But a lot of what Kleiner wrote in 1998 about fitness nutrition still holds up 22 years later.