Yet Another Low Carb Performance Study

Here’s another study which looked a performance on a Low Carb diet (Sawyer, JC, Wood, RJ, Davidson, PW, Collins, SM, Matthews, TD, Gregory, SM, and Paolone, VJ. Effects of a short-term carbohydrate-restricted diet on strength and power performance. J Strength Cond Res 27(8): 2255–2262, 2013).

For this study 16 men and 15 women were tested after a week on their habitual diet (40.7% carbohydrate, 22.2% protein, and 34.4% fat) and then a week later on a Carbohydrate Restricted Diet (CRD – 5.4% carbohydrate, 35.1% protein, and 53.6% fat). The CRD consisted of ≤50 g of carbohydrates per day.

The study was intended to determine if strength is lost with the short diet timeframe. The results were:

Subjects consumed significantly fewer (p < 0.05) total kilocalories during the CRD (2,156.55 ± 126.7) compared with the habitual diet (2,537.43 ± 99.5).

That can be seen here:

That’s less than 400 calories a day or 2800 calories for the seven days. This may be due to the following:

During the CRD, the researcher contacted each subject every 48 hours to answer any questions about the diet. Body weight was measured every 48 hours during the CRD to determine if any body mass changes had occurred. If a reduction in body weight occurred during the CRD, subjects were instructed to consume more calories to maintain body weight.

Continuing with the results.

Body mass decreased significantly (p < 0.05).

Fortunately this study showed the Total body water. This indicates that most of the FFM loss was due to water loss and seemed to be the only significant effect.

Both males and females had improved body fat composition.

Despite a reduction in body mass, strength and power outputs were maintained for men and women during the CRD.

One big advantage of this study was the goal of keeping calories enough to not have losses. That’s relevant to people on keto consuming maintenance calories.

A major weakness was the short duration of the study. We can’t say that seven days isn’t enough time for adaptation in some studies and that it is enough time in other studies, can we?

Another weakness was the lack of a control group. It would have been helpful to have part of the group stay on the habitual diet during the second period.

A third weakness was the same before and after the keto adaptation phase:

Before each testing session, subjects were required to refrain from performing resistance exercise for 48 hours.

A forth weakness was that:

Participants arrived at the Human Performance Laboratory after a 12-hour fast between the hours of 6:00 and 8:00 AM.

They were then fed a fat/protein meal.

The pre-exercise meal was provided to each subject 2 hours before the start of each exercise testing session. The meal consisted of 400 kcal. The meal included 250 ml of water, 2 hard-boiled eggs, 28 g of cheddar cheese, and a protein shake (Advant Edge Whey Protein; EAS, Inc., Abbott Park, IL, USA).

It seems likely that this meal would be more useful to the athletes after keto adaptation than before. Again a control group would have teased out this difference.

Conclusions

Most of the tests were very short duration – One Rep Maximums and short erg bicycles. Only one was to exhaustion and there was a lot of rest between sets (3 minutes). The Keiser power output was lower with the keto diet but judged to not be significant. That is a surprise to me since the change was greater than the error bars.

I would expect the keto athletes to do reasonably well with the short duration of the tests. Without a control group it is difficult to determine if the group should have gotten stronger or not.

 

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