<p>I'm not sure what you mean to ask here, but there is a recent (2016) meta-analysis by <a href="http://doi.org/10.1177/0956797616654911" rel="nofollow noreferrer">Vadillio, Gold and Osman</a> just on the topic of glucose and willpower. Abstract:</p>

<blockquote>
  <p>The idea behind ego depletion is that willpower draws on a limited mental resource, so that engaging in an act of self-control impairs self-control in subsequent tasks. To present ego depletion as more than a convenient metaphor, some researchers have proposed that glucose is the limited resource that becomes depleted with self-control. However, there have been theoretical challenges to the proposed glucose mechanism, and the experiments that have tested it have found mixed results. We used a new meta-analytic tool, p-curve analysis, to examine the reliability of the evidence from these experiments. We found that the effect sizes reported in this literature are possibly influenced by publication or reporting bias and that, even within studies yielding significant results, the evidential value of this research is weak. In light of these results, and pending further evidence, researchers and policymakers should refrain from drawing any conclusions about the role of glucose in self-control.</p>
</blockquote>

<p>It's not too far in its conclusions from <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4115664/" rel="nofollow noreferrer">a 2014 meta-analysis on the mere existence of ego/willpower depletion</a>. </p>

<p>As Vadillo et al. use <a href="http://p-curve.com" rel="nofollow noreferrer">p-curves</a>, the interpretation of their result is somewhat subjective.</p>

<p><a href="https://i.sstatic.net/mp02d.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/mp02d.png" alt="enter image description here"></a></p>

<p>Here is their interpretation:</p>

<blockquote>
  <p>The results of our analyses suggest that the relationship
  between glucose levels and self-control behaviors might
  be unreliable. Figure 1 shows that the key p values of the
  19 studies included in the present analyses follow a surprisingly
  flat distribution. This is exactly the pattern of
  results that one would expect to find if those results were
  false positives. These results remain unchanged regardless
  of whether glucose-rinsing studies are included or
  excluded from the sample.
  These results may not come as a complete surprise
  given the empirical challenges to the glucose hypothesis
  suggested by failed replications (Job et al., 2013; Kelly
  et al., 2015; Lange &amp; Eggert, 2014; Lange et al., 2014) and
  theoretical critiques regarding its biological plausibility
  (Kurzban, 2010; Osman, 2014). Furthermore, a detailed
  analysis of the seminal article suggesting the glucose
  hypothesis showed that the number of significant findings
  reported in that article was too large, given the low
  power of each study (Schimmack, 2012). In other words,
  the results were too good to be true (Francis, 2012).
  Nevertheless, the findings from the present study are a
  surprise in the context of the wide acceptance of the
  glucose hypothesis in general scientific research and its
  popularity, as evidenced by the number of citations of
  Gailliot et al. (2007) in the literature and the continued
  influence of this hypothesis in recent reviews on ego
  depletion (e.g., Baumeister, 2014; Baumeister &amp; Alghamdi,
  2015).</p>
  
  <p>[...]</p>
  
  <p>It is worth noting that, as with any other statistical test,
  p-curve analysis is not a flawless indicator of bias (Bishop
  &amp; Thompson, 2016; Bruns &amp; Ioannidis, 2016; Lakens,
  2015). Our results suggest that, on average, these studies
  have little or no evidential value, but they do not allow
  us to determine whether the significant results are due to
  publication bias, selective reporting of outcomes or analyses,
  p-hacking, or all of these. It is not impossible that
  some of these studies are exploring small but true effects
  and that their evidential value may be diluted by the
  biases that pervade the rest of the studies. Perhaps future
  research will show that glucose does play a role in egodepletion
  effects, but our conclusions are based on the
  analysis of the extant literature in this area. Thus, our
  contribution must be seen as an additional piece of information
  in the wider context of attempts to verify the reliability
  of the glucose model of ego depletion. Note that
  the kind of biases explored in the present study are prevalent
  in other (but not all) areas of psychological research
  (e.g., Bakker, van Dijk, &amp; Wicherts, 2012) and that low
  reproducibility is not exclusively a problem of psychological
  research (Camerer et al., 2016; Errington et al.,
  2014). </p>
</blockquote>

<hr>

<p>The meta-analysis had a special category for glucose-rinsing studies:</p>

<blockquote>
  <p>Glucose-rinsing studies examine the impact of simply
  rinsing one’s mouth with a glucose solution
  before exerting self-control (Hagger &amp; Chatzisarantis,
  2013; Lange &amp; Eggert, 2014; Molden et al., 2012;
  Sanders, Shirk, Burgin, &amp; Martin, 2012). Results
  from these studies suggest that the signal of glucose
  from the mouth to the brain is sufficient to
  neutralize the ego-depletion effect. This mechanism
  is consistent with the results of the ingestion
  manipulations but suggests that the effect does not
  depend on a metabolic explanation.</p>
</blockquote>

<p>Here's the full table of studies included, which included an indicator column for whether the study was rinsing-only:</p>

<p><a href="https://i.sstatic.net/tR0ha.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/tR0ha.png" alt="enter image description here"></a></p>

<p>But there's no separate p-curve just for the rinsing studies. You can probably make one yourself though...</p>

<p>Actually I just did that with the 8 studies in the "yes" column:</p>

<p><a href="https://i.sstatic.net/hKcB9.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/hKcB9.png" alt="enter image description here"></a>
<a href="https://i.sstatic.net/A8pcQ.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/A8pcQ.png" alt="enter image description here"></a></p>

<p>Note that they've changed the test somewhat since that meta-analysis was published.</p>

<p>The meta-analysis did note that whether the rinsing studies were added or removed made no difference on the p-curve testing of the rest. And from my graph you can kinda see why: ignoring the 0% bins, the rinse group has roughly the same shape as the whole group.</p>

CC BY-SA 3.0
2018-01-03T11:48:26.277Z
The claim I'm asking about is not the direct "glucose levels -> willpower" but a modified "taste of sugar -> willpower". It possible for the second one to be true while the first one is false.
Given that papers like this show that the first hypothesis is likely false it becomes interesting to know whether the second one is true.
Christian
CC BY-SA 3.0
2018-01-03T03:02:35.137Z
2018-01-03T12:53:00.887Z
2018-01-03T12:53:00.887Z
got trolled too much this week
<p>In a post titled <a href="https://www.lesserwrong.com/posts/XKfQF73YnyMRiRf9a/willpower-depletion-vs-willpower-distraction" rel="nofollow noreferrer">Willpower Depletion vs Willpower Distraction</a> the claim is made that:</p>

<blockquote>
  <p>Basically, for a while some researchers believed that willpower
  depletion "is" glucose depletion in the prefrontal cortex, but some
  more recent experiments have failed to replicate this, e.g. by finding
  that the mere taste of sugar is enough to "replenish" willpower faster
  than the time it takes blood to move from the mouth to the brain:</p>
</blockquote>

<p>Is that claim representative of the knowledge we have from studies?</p>

CC BY-SA 3.0
2018-01-03T02:02:13.397Z
Isn't the blog quoting (and citing) some papers right after that paragraph? Are you asking if he's misrepresenting them or if there also exist studies to the contrary? For the Wikipedia take on this: https://en.wikipedia.org/wiki/Ego_depletion#Physiological_causes
got trolled too much this week
CC BY-SA 3.0
2018-01-03T02:17:09.383Z
And I think Wikipedia has missed one interesting paper on the topic: http://www.pnas.org/content/110/37/14837.full
got trolled too much this week
CC BY-SA 3.0
2018-01-03T02:29:26.387Z
Wikipedia also fails to mention failed replication attempts such as https://jeps.efpsa.org/articles/10.5334/jeps.cc/ But this is somewhat typical on a rather obscure topic like this. On the other hand, Wikipedia does cite https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4115664/
got trolled too much this week
CC BY-SA 3.0
2018-01-03T11:55:19.987Z
@Fizz : The blog is quoting papers from 2004/2009. I'm interested on whether the finding that while glucose consumption doesn't lead to willpower replenishment, tasting sugar does, holds up in more recent papers.
Christian
CC BY-SA 3.0
2018-01-03T13:19:32.990Z
The blog is also citing Molden et al., which is from 2012, although the blog failed to give a year for Molden's paper.
got trolled too much this week
CC BY-SA 3.0
2018-01-03T13:27:03.857Z
And how can consumption not lead to replenishment if it's by ingestion and tasting is enough to cause replenishment? Doesn't (oral) consumption entail tasting? Are there intravenous administration studies? And are they the majority? That's pretty doubtful since these studies are overwhelmingly done by psychologists who'd lack the personnel for other routes of administration. So the blog's conclusion is weird. " failed to replicate this, e.g. by finding that the mere taste of sugar is enough to "replenish" willpower" is basically an invalid line of reasoning.
got trolled too much this week
CC BY-SA 3.0
2018-01-03T13:32:41.417Z
He probably wanted to say that there was an alternative explanation for the ingestion studies provided by the mere tasting studies rather than "failure to replicate"... although that also happened, but not in the studies cited in the blog post itself (there is one such true-failure-to-replicate study in the readers' comments though).
got trolled too much this week
CC BY-SA 3.0
2018-01-03T13:41:23.200Z
@Fizz : Molden et al contains a passage saying "Indeed, one study demonstrated that carbohydrate rinsing had a greater effect on performance than carbohydrate ingestion did"
Christian
CC BY-SA 3.0
2018-01-03T13:41:57.537Z
I'm guessing they could use a coated pill (so it doesn't taste) and a placebo one... Alas the meta-analysis I found din't separate non-tasting studies (i.e. where the Ss had no way of tasting what they were ingesting.)
got trolled too much this week
CC BY-SA 3.0
2018-01-03T13:45:45.423Z
Given that the whole field of rinse is more explanatory (never mind produces stronger effects) consists of 3 papers, including Molden's, there's not much else I can say than: believe them if you want. Their p-curve doesn't look any better than for the ingestion studies though (see end of my answer).
got trolled too much this week
CC BY-SA 3.0
2018-01-03T14:09:04.573Z
Interesting that study with "greater" claims, [Pottier et al.](https://www.ncbi.nlm.nih.gov/pubmed/19000099) is not ostensibly about willpower. I'm guessing this is why it's not included in the meta-analysis. I've looked at the Pottier study; it's about short but intense exercise with zero mention of willpower or ego. Molden is making rather wild claims of relevance of short-term physical exercise papers to his own problem.
got trolled too much this week
CC BY-SA 3.0
2018-01-03T14:20:46.490Z
Note that experiment 4 from Molden (rinse vs. ingestion) is not included in the meta-analysis either because it had no placebo/control. I'm not sure anyone else attempted to replicate this experiment 4 of Molden. Not only that, but Molden's paper
fails to report whether rinse was better than ingestion in his experiment 4. He just says he noted an interaction in a 2x2 ANOVA, but doesn't cleary say in which direction!
got trolled too much this week
CC BY-SA 3.0
2018-01-03T14:28:08.793Z
Ah, the 2x2 ANOVA in that experiment 4 was... (condition: ingest vs. rinse) × (glucose assessment: pre-task vs. posttask). Very, very oddly no attempt was made to discern whether ingestion was better or worse than rinse in its effect *on the actual task*. My guess: they tested, but didn't like what they saw.
got trolled too much this week
<willpower>
Does the taste of sugar replenish willpower?
Christian
# Does the taste of sugar replenish willpower?

(Asked by: username_0 on 2018-01-02)

In a post titled [Willpower Depletion vs Willpower Distraction](https://www.lesserwrong.com/posts/XKfQF73YnyMRiRf9a/willpower-depletion-vs-willpower-distraction) the claim is made that:

> Basically, for a while some researchers believed that willpower
> depletion "is" glucose depletion in the prefrontal cortex, but some
> more recent experiments have failed to replicate this, e.g. by finding
> that the mere taste of sugar is enough to "replenish" willpower faster
> than the time it takes blood to move from the mouth to the brain:

Is that claim representative of the knowledge we have from studies?

**Tags:** willpower

> **Comments:**
> **username_1**: Isn't the blog quoting (and citing) some papers right after that paragraph? Are you asking if he's misrepresenting them or if there also exist studies to the contrary? For the Wikipedia take on this: https://en.wikipedia.org/wiki/Ego_depletion#Physiological_causes  
> **username_1**: And I think Wikipedia has missed one interesting paper on the topic: http://www.pnas.org/content/110/37/14837.full  
> **username_1**: Wikipedia also fails to mention failed replication attempts such as https://jeps.efpsa.org/articles/10.5334/jeps.cc/ But this is somewhat typical on a rather obscure topic like this. On the other hand, Wikipedia does cite https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4115664/  
> **username_0**: @Fizz : The blog is quoting papers from 2004/2009. I'm interested on whether the finding that while glucose consumption doesn't lead to willpower replenishment, tasting sugar does, holds up in more recent papers.  
> **username_1**: The blog is also citing Molden et al., which is from 2012, although the blog failed to give a year for Molden's paper.  
> **username_1**: And how can consumption not lead to replenishment if it's by ingestion and tasting is enough to cause replenishment? Doesn't (oral) consumption entail tasting? Are there intravenous administration studies? And are they the majority? That's pretty doubtful since these studies are overwhelmingly done by psychologists who'd lack the personnel for other routes of administration. So the blog's conclusion is weird. " failed to replicate this, e.g. by finding that the mere taste of sugar is enough to "replenish" willpower" is basically an invalid line of reasoning.  
> **username_1**: He probably wanted to say that there was an alternative explanation for the ingestion studies provided by the mere tasting studies rather than "failure to replicate"... although that also happened, but not in the studies cited in the blog post itself (there is one such true-failure-to-replicate study in the readers' comments though).  
> **username_0**: @Fizz : Molden et al contains a passage saying "Indeed, one study demonstrated that carbohydrate rinsing had a greater effect on performance than carbohydrate ingestion did"  
> **username_1**: I'm guessing they could use a coated pill (so it doesn't taste) and a placebo one... Alas the meta-analysis I found din't separate non-tasting studies (i.e. where the Ss had no way of tasting what they were ingesting.)  
> **username_1**: Given that the whole field of rinse is more explanatory (never mind produces stronger effects) consists of 3 papers, including Molden's, there's not much else I can say than: believe them if you want. Their p-curve doesn't look any better than for the ingestion studies though (see end of my answer).  
> **username_1**: Interesting that study with "greater" claims, [Pottier et al.](https://www.ncbi.nlm.nih.gov/pubmed/19000099) is not ostensibly about willpower. I'm guessing this is why it's not included in the meta-analysis. I've looked at the Pottier study; it's about short but intense exercise with zero mention of willpower or ego. Molden is making rather wild claims of relevance of short-term physical exercise papers to his own problem.  
> **username_1**: Note that experiment 4 from Molden (rinse vs. ingestion) is not included in the meta-analysis either because it had no placebo/control. I'm not sure anyone else attempted to replicate this experiment 4 of Molden. Not only that, but Molden's paper fails to report whether rinse was better than ingestion in his experiment 4. He just says he noted an interaction in a 2x2 ANOVA, but doesn't cleary say in which direction!  
> **username_1**: Ah, the 2x2 ANOVA in that experiment 4 was... (condition: ingest vs. rinse) × (glucose assessment: pre-task vs. posttask). Very, very oddly no attempt was made to discern whether ingestion was better or worse than rinse in its effect *on the actual task*. My guess: they tested, but didn't like what they saw.  

---

## 1 answers

### Answer by username_1 on 2018-01-03. Score: 4

I'm not sure what you mean to ask here, but there is a recent (2016) meta-analysis by [Vadillio, Gold and Osman](http://doi.org/10.1177/0956797616654911) just on the topic of glucose and willpower. Abstract:

> The idea behind ego depletion is that willpower draws on a limited mental resource, so that engaging in an act of self-control impairs self-control in subsequent tasks. To present ego depletion as more than a convenient metaphor, some researchers have proposed that glucose is the limited resource that becomes depleted with self-control. However, there have been theoretical challenges to the proposed glucose mechanism, and the experiments that have tested it have found mixed results. We used a new meta-analytic tool, p-curve analysis, to examine the reliability of the evidence from these experiments. We found that the effect sizes reported in this literature are possibly influenced by publication or reporting bias and that, even within studies yielding significant results, the evidential value of this research is weak. In light of these results, and pending further evidence, researchers and policymakers should refrain from drawing any conclusions about the role of glucose in self-control.

It's not too far in its conclusions from [a 2014 meta-analysis on the mere existence of ego/willpower depletion](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4115664/).

As Vadillo et al. use [p-curves](http://p-curve.com), the interpretation of their result is somewhat subjective.

[![enter image description here](https://i.sstatic.net/mp02d.png)](https://i.sstatic.net/mp02d.png)

Here is their interpretation:

> The results of our analyses suggest that the relationship
> between glucose levels and self-control behaviors might
> be unreliable. Figure 1 shows that the key p values of the
> 19 studies included in the present analyses follow a surprisingly
> flat distribution. This is exactly the pattern of
> results that one would expect to find if those results were
> false positives. These results remain unchanged regardless
> of whether glucose-rinsing studies are included or
> excluded from the sample.
> These results may not come as a complete surprise
> given the empirical challenges to the glucose hypothesis
> suggested by failed replications (Job et al., 2013; Kelly
> et al., 2015; Lange & Eggert, 2014; Lange et al., 2014) and
> theoretical critiques regarding its biological plausibility
> (Kurzban, 2010; Osman, 2014). Furthermore, a detailed
> analysis of the seminal article suggesting the glucose
> hypothesis showed that the number of significant findings
> reported in that article was too large, given the low
> power of each study (Schimmack, 2012). In other words,
> the results were too good to be true (Francis, 2012).
> Nevertheless, the findings from the present study are a
> surprise in the context of the wide acceptance of the
> glucose hypothesis in general scientific research and its
> popularity, as evidenced by the number of citations of
> Gailliot et al. (2007) in the literature and the continued
> influence of this hypothesis in recent reviews on ego
> depletion (e.g., Baumeister, 2014; Baumeister & Alghamdi,
> 2015).
>
> [...]
>
> It is worth noting that, as with any other statistical test,
> p-curve analysis is not a flawless indicator of bias (Bishop
> & Thompson, 2016; Bruns & Ioannidis, 2016; Lakens,
> 2015). Our results suggest that, on average, these studies
> have little or no evidential value, but they do not allow
> us to determine whether the significant results are due to
> publication bias, selective reporting of outcomes or analyses,
> p-hacking, or all of these. It is not impossible that
> some of these studies are exploring small but true effects
> and that their evidential value may be diluted by the
> biases that pervade the rest of the studies. Perhaps future
> research will show that glucose does play a role in egodepletion
> effects, but our conclusions are based on the
> analysis of the extant literature in this area. Thus, our
> contribution must be seen as an additional piece of information
> in the wider context of attempts to verify the reliability
> of the glucose model of ego depletion. Note that
> the kind of biases explored in the present study are prevalent
> in other (but not all) areas of psychological research
> (e.g., Bakker, van Dijk, & Wicherts, 2012) and that low
> reproducibility is not exclusively a problem of psychological
> research (Camerer et al., 2016; Errington et al.,
> 2014).

---

The meta-analysis had a special category for glucose-rinsing studies:

> Glucose-rinsing studies examine the impact of simply
> rinsing one’s mouth with a glucose solution
> before exerting self-control (Hagger & Chatzisarantis,
> 2013; Lange & Eggert, 2014; Molden et al., 2012;
> Sanders, Shirk, Burgin, & Martin, 2012). Results
> from these studies suggest that the signal of glucose
> from the mouth to the brain is sufficient to
> neutralize the ego-depletion effect. This mechanism
> is consistent with the results of the ingestion
> manipulations but suggests that the effect does not
> depend on a metabolic explanation.

Here's the full table of studies included, which included an indicator column for whether the study was rinsing-only:

[![enter image description here](https://i.sstatic.net/tR0ha.png)](https://i.sstatic.net/tR0ha.png)

But there's no separate p-curve just for the rinsing studies. You can probably make one yourself though...

Actually I just did that with the 8 studies in the "yes" column:

[![enter image description here](https://i.sstatic.net/hKcB9.png)](https://i.sstatic.net/hKcB9.png)
[![enter image description here](https://i.sstatic.net/A8pcQ.png)](https://i.sstatic.net/A8pcQ.png)

Note that they've changed the test somewhat since that meta-analysis was published.

The meta-analysis did note that whether the rinsing studies were added or removed made no difference on the p-curve testing of the rest. And from my graph you can kinda see why: ignoring the 0% bins, the rinse group has roughly the same shape as the whole group.

> **Comments:**
> **username_0**: The claim I'm asking about is not the direct "glucose levels -> willpower" but a modified "taste of sugar -> willpower". It possible for the second one to be true while the first one is false. Given that papers like this show that the first hypothesis is likely false it becomes interesting to know whether the second one is true.  

---

